I use one on my 5D2. Originally bought it for my 7D and was one of my favourite lenses on that - I've taken some of my favourite photos with this lens. When I bought my 5D2 I considered changing it for a 17-40L or 16-35L but after research decided to keep it as its generally regarded as a better performer than the Canon lenses, especially when it comes to corner sharpness. The only downside is that it vignettes before around 17-18mm so it effectively reduces the focal range, but 17mm is very wide on FF!
I can't post any pics taken with it on my 5D2 as I'm on holiday - might be able to check on my Flickr a bit later on.