Conclusion: I bought this lens after my extreme satisfaction with EF 14mm f/2.8L II USM. I wanted a lens that corrects the super wide angle distortion effect. I took this lens with me to Paris and used it to photograph cathedrals and buildings. After few attempts, I was able to control focusing without then need of a tripod and captured tall structures up close with virtually no distortion.
Conclusion: I have these lens to use it in architectural photography, but the amazing thing it's that you can do a lot of things with it. It gives you a lot of possibilities to expand your imagination. Now I use it everywhere I go, for example I go to vacations to Las Vegas with family and I take amazing photos from the city and family only with these lens.
Pros: image quality, feels very solid, lots of possibilities, focus ring is very precise
Cons: bulky, heavy, no af, front lens needs care, lens cap is bulky too
Conclusion: I've now owned the 17mm TS mounted on a Canon 5D MarkII for several months shooting home interiors for the Real Estate market. My 'backup' lens is now my 7D with a Canon 10-22mm lens, which is my comparison setup. I will not go into detail here as many others have already provided that type of excellent feedback. This lens is simply awesome and does what the top-notch 10-22mm lens could not do.
Conclusion: I've been an architectural shooter for over 20 years. I've been through several wide lenses starting with the 20mm, then the 17-35, 17-40, 16-35 and I currently have the 16-35 Mark II. While it's the best of the zooms and better than the fixed 20mm, it can't even come close in image quality to the TS-E 17mm. The only thing lacking is the ability to polarize this lens, which is something I do quite often when shooting interiors.
Pros: super sharp to the edges, tilt shift, low flare, low c.a., low distortion