Love this lens.

I've used the Tokina 100mm AT-X Pro for a couple years now and I simply love it. I shoot lots of smaller wildlife - lizards, frogs, snakes, insects, etc. - and this lens is perfect for it. Since it's 100mm, it allows you to get some nice shots of venomous snakes from a safe distance.

The feel and finish on the lens is excellent; it simply looks great, like a serious high-end lens. The lens is solid, and doesn't have that "cheap" feel that some lenses get. The trade-off is that the lens is a bit heavier than some of its alternatives (Sigma, Tamron), but they're all so close in weight that I don't think this is really an issue.

Images come out great with this lens: sharp with true colors (be sure to invest in a decent haze/UV filter if you use one...don't want to handicap your lens!). Admittedly, I typically sharpen my shots with PP, but that is an issue with digital cameras, not the lens. Oh, and it's a "full frame" lens (an FX lens for Nikon shooters), so you can use it with the higher end full-frame cameras as well as the typical DX cameras.

Price on this lens is around $450 US, I think. I don't regret my purchase for a second. In fact, I'm so happy with my Tokina macro that I'm now looking around for a wide-angle and Tokina is at the top of my list.

Problems:

Tough to come up with problems for this lens, but to be fair, I'll list some minor things. I mentioned that it's a bit heavy. For me, this simply is not an issue. I don't use the lends for all around shooting, so I rarely carry it around all day. Even when I do, I just don't really think about the weight.

Focusing can seem a little slow in low light (go figure), but I haven't used the Tamron or Sigma macros, so this may just be the nature of the beast at this focal length. And the drive seems a bit loud when focusing, but this isn't something I think about when I'm shooting.

Finally, realize this lens apparently won't autofocus with the lower-end Nikons (I don't know about other camera brands). I use a D90 and it works fine.