I went straight from shooting with Nikon film cameras to the Canon 5D 2 years ago for professional projects. I have to say that I'm a fan!
Why the 5D? Apart from the build quality, I chose the 5D over the 1DsII at the time because the final image quality between the 2 cameras was not enough to warrant the extra cost, even though it was not much of an issue. I shoot everything from fashion, food, portraits, industrial and product photography. Occasional wedding photography if time allows. With all these projects I've never found the 5D wanting, even action/sports to a point.
Using L series lenses is a must to get the most out of this camera, and for my purposes (print media) it's never disappointed me or my clients. Post production of RAW files in PS CS3 is fantastic.
As with any tool, knowing your equipment is vital to getting the best out of it and the 5D is a pleasure to use once familiar with it. It's the type of camera where your only limit is your imagination.
All I need to get now is a 14mm L wide angle and I'm set. Just upgrade the body when necessary.
I'm looking forward to the 5DII due shortly!