This is not a technical review. Just my personal observations. I've been taking pictures since I was 21 -- Pentax Spotmatic and then Canon F-1. I'm not a professional but I think I know what a good image looks like.
I purchased this lens with some trepidation. First the price did not indicate a great lens and there were some iffy reviews. Also it doesn't have VR. I took a chance and bought it to replace a lens that didn't have enough range. Its mounted on my D300. Frankly, if Tokina made this with a mount for equipment that had in camera stabilization it would be just about perfect.
This lens is very compact, and the smallest available in this range. You can handhold this lens with most applications or use a monopod if walking around. While it doesn't have VR, the long lenses that do are bazookas compared to this so that more or less cancels things out. One simply could not handhold the Nikon 80-400 (I know -- I tried); the Sigma 120-400 or 150-500 are also much too large to handhold.
This lens if very sharp except at the extreme 400 range where it gets a little soft, and that doesn't make much difference because sharpening in processing fixes that (distinguish here between the fact that the lens is a little soft at this range as opposed to shaky hands).
This lens even works with the Kenko 2x converter, but you have to have a good tripod and use good tripod technique (effective 1200 mm with the 1.5 crop factor -- any lens will be difficult). By the way, there is some discussion that the AF and metering will not work with the converter. Mine works just fine -- you simply have to have bright sun and use spot metering (Matrix has a hard time). My understanding is that the Nikon does not work with a converter (unless maybe its the super expensive Nikon version).
It is a slow lens, so you have to have a lot of light (not a problem in Arizona). If you are at the lower end and your image is not too far away, the on camera flash will work for fill light. This may be because the lens itself is very compact so does not interfere with the flash. I did this today inside an aviary at the zoo.
At the zoo today, intermittent sun and clouds. Using the bracketing function resulted in many fine images.
The build quality is remarkable for a lens in this price range. I know Tokinas get pretty good reviews, but I think you could pound nails with this. And, because of its size (and resulting reduced weight), you can carry this all day. I know; I just did.
All in all, this is a great lens for the money. Its much more lens for the money. I gave it 5 stars because its better than advertised. It doesn't purport to be what it is not -- its not a ,000 lens. Its a good substantial lens. You would have to put down some serious bucks to get a better combination and versatility. It doesn't have VR. I think a VR in this range would be so much larger (and they seem to be) that you could not handhold it anyway.
Couple this lens with the 16-85 VR and the 50/1.8 (with some close up diopters) and you have a fine amateur kit without losing your entire inheritance.
Average Rating:

Brand: Tokina
Model: AF 80-400mm
Product Description:
Tokina 80-400/4.5-5.6 AT-X 840 D Telephoto Zoom Lens for NIkon D USA
Features: 80-400/4.5-5.6 AT-X 840 D Telephoto Zoom Lens for NIkon D USA
Available at Amazon
Lowest Used Price: USD 485.00
Lowest New Price: USD 499.00

Customer Reviews

Good lens with some concerns.
I had this lens for a few months and tested it at different focal lengths. Here is the break down of things I find about this lens:
Pros:
1. It is the cheapest and lightest lens available for nikon lens at 400mm.
2. The build is solid.
3. The lens hood has a little wheel for you to rotate the filter when you have such as a cpl filter on the lens with the hood on.
4. There is a ring attached to the lens so that you can rotate the camera+lens on a tripod easily.
5. Sharpness is very good with any focal length shorter than or equal to 350mm.
Cons:
1. Sharpness at 400mm is soft. The pictures are almost unacceptable if taken by handheld. However, using a tripod will solve part of the problem, and stopping down to at least f8 will somewhat help as well. BTW, you should shoot with a tripod anyway with such a heavy lens. So my suggestion is to stop down to at least f8 and shoot on a tripod if you want to go to 400mm with this lens. (This statement is not totally true, see the P.S. section for more info)
2. Chromatic aberration is quite obvious with this lens up to 400mm. Compare to my Nikon 18-200mm vr lens, this lens produce significantly more chromatic aberration. I found significant longitudinal and lateral chromatic aberration at even f8 at 400mm. The pictures have mostly either "green fringing" or "blue fringing" instead of "purple fringing" which is usually associated with the camera sensor. I kind of look at the internal glasses design of this lens from Tokina's website. It seems that they use achromatic doublet to improve the color fringing, and it is claimed that the glasses are multi-coated. However, this is still my biggest concern.
One thing I have not tried is to shoot subjects in motion with this lens, so I can't say how fast this lens can be.
P.S.:
7/04/09, I will correct my previous statment that shooting handheld with this lens produce unacceptable images, even at the 400mm end. I think I used my 18-200mm VR lens so often that I can take most static or moving subjects at speed around 1/100 sec. (when the maximum focal length is 200mm) with no sharpness problem. The VR property kind of defys the old rule about the fact that you have to shoot at the speed of at least 1/focal length, and blinded me from following the old rules. I have been shooting again handheld with this lens today. After I came home to look at the images carefully, I realize that some of images look sharp and some don't even when they are taken at the same focal length. The only difference is that they are taken at different speeds. I did more testing and found that even at 400mm, you can get reasonably sharp images with static subjects when you set your shutter at 1/640 sec or faster at handheld. So, it was my technique, not the lens that produce poor results, and it reminds me again that THIS IS NOT A VR LENS and you have to apply the old rules on this lens, especially at 400mm. My final conclusion, you can get sharp picture with this lens even at 400mm if you use it properly.

Practical!
I bought this lens last year and I have been using it since then. I use it virtually indoors and outdoors preferably "sunny". I must admit, I am using my SB800 flash when I am indoor. This lens is a perfect match with the Nikon D300 you can play with the setting you like. Manual setting will give the best exposure in my own experience. For me the lens works very well with manual setting. Use a monopod when using it in events, your arm will get tired. The only downside is the lock that does'nt work. All in all I'm very satisfied with this lens. It's money's worth.

The most compact 80-400
I have had this lens for over a year and i shot some really good pictures with it. It is by far the most compact 80-400 in the market and the sharpness and the colors are lot better than what you would expect from a third party manufacturer. (I also have the tokina 12-24 and that is also really good)
The built Quality is Great it is solid, when you hold it you feel metal not some plastic. I also have the sigma 50-150 and it has HSM so one day while i was shooting some birds in flight i said to myself because tokina does not have an internal focus and focuses slower than a hsm sigma the sigma would be a better choice. man i was wrong. after shooting an hour with the sigma i decided to give tokina a try and it was much better. even though the focus was not as fast it was fast enough to catch birds and the 80-400 range was so much better than 50-150. on a D300
If you are looking for a budget 80-400 do not even hesitate and buy this lens.