I own both consoles.  Xbox Live is a credit to the 360 and is truely the better on-line service,  although PSN is free and tends to be less laggy then Xbox Live.  Xbox Live is packed with demos movies and other downloads including voice chat in every on-line game,  PSN has these just not as many.  Also IMO the Xbox Live Arcade is reason enough to purchase a 360.  Systems itself Xbox 360 was VERY well thought out.  It's OS has awesome features such as checking messages, friends, and a MP3 while in any game.  The Xbox Dashboard just has a flow to it not found on the PS3.  While the PS3 tends to be less user friendly I can honestly say I can tell a noticable difference in graphics with the PS3 showing more next gen.  Only complaint I have with my PS3 is how the friends list seems almost non function in none of the games I have use it. 

In short, If I could only have one console it would be the Xbox 360 but owning both is well worth it.