I love my 17-40 on my crop. I am a little concerned about the corners on a full frame (5diii coming soon!). Do the thin mount filters make much of a difference? I have my doubts about this lens being upgraded anytime soon and the TS-E 17 would be a pricey fix (but an awesome one!).
On FF 17-40 requires a thin filter. Here http://www.canonrumors.com/forum/index.php/topic,3729.msg79202.html#msg79202 I have posted en example of how bad it is when NOT having a thin filter.