Long story short: I am very pleased with the Tokina 10-17. I've used it quite a lot ofer the last few weeks and soon discovered that it is not by any means a toy or just a novelty lens.
Here is one from yesterday. (20D, 17mm, ISO 200, f/13, 1/250th.)
Keeping the camera horizontal is absolutely critical unless you want to do weird, distorted stuff, but if you do that, it works very well indeed. Sharp as you like, and nice bright colours.
Here is another: (20D, 11mm, ISO 200, f/16, 1/200th.)
And one from last month: (20D, 17mm, ISO 200, f/8, 1/2000th.)
It flares more than my other ultra-wide (the Canon EF-S 10-22) but, as you can see, is nevertheless mostly very good. It does sometimes do some weird stuff with flare (I'll try to find an example to post when I get a spare moment) but I am shooting directly into the sun, which is a pretty hard ask of any lens.
These three samples by the way are all un-cropped and un-processed, just JPGs straight out of the camera shot very flat - perhaps a little over-flat, I usually dial down the saturation in-camera and add it back in PP, but for demonstration purposes with these three I have left the JPG unaltered.