Testing 5D MkII with 17mm TSE PC lens. It's a great camera and a great lens but it's not as useful as 24mm. I use PC lenses with Nikon D3X and must say that it's a great combination, plus D3X beats Canon when it comes down to image quality. The difference is huge, but I love the versatility of 5D MkII and the fact that it produces stunning HD when handled properly.
Check out Redrock micro website for advanced DSLR video accessories. Coming back to Canon's 17mm TSE, the obvious problem is that humongous glass and how it handles glares in some light situations. It's not cheap either, but in many cases it seems a necessary tool for architectural photography and landscapes. For those in favor of less extreme PC lenses the following link provides information on the new and improved Canon 24mm TSE. Enlarged image circle and overall sharpness - for more details read what dp review has to say about it.

photo: © Slav Zatoka, Griffith Observatory