I have both. I had an XBox for about 3 years, had it replaced once due to the red ring. I also recently bought one of the new slim PS3's with a 160 GB drive. It was cheaper than the Sony Blu-Ray player I was considering buying.
One thing I like about the PS3 is it takes only a few seconds to start the system up and play the game vs several minutes on my PS2. I think the interface is better too.
Graphics on the other hand seem a lot better on the XBox. I have Madden 2008 on my XBox and Madden 2009 on my PS3. The Godfather on my XBox, and Godfather II on my PS3. Both XBox games have better looking graphics than the PS3 games, but that might be the graphic engines used in the games more than the systems itself. Although compared to my PC the graphics on both systems are a bit outdated. Hopefully newer consoles come out in a year or too.
Blu-Ray's play great on my PS3, but I wouldn't want to use it without purchasing the Blu-Ray controller.
The game controllers for both are about the same, but I like the feel of the XBox's better. The PS3's seems a bit too small in my hands. I have played with the Wii and wish that the XBox and PS3's had a similar controller.