The decision all comes down to the preference of games. Sony has always had better RPGs on their consoles. Xbox has always had plenty of shooters. Good games are on both consoles it just depends on your taste. I initially bought my PS3 so I could play MGS4 and Disgaea 3 and Resistance 2, all PS3 exclusives. I initially got my Xbox 360 so I could play Gears of War and Chromehounds, again exclusives. All of these are good games and tailor to different types of people.
XBL is a paid-for service that gives an excellent lag free (usually) online experience. PSN is free but you have to deal with people that can lag so bad the console crashes (happened to me on LBP).
The Dualshock 3 is about as heavy as the 360 controller so you can't argue, if you have a sixaxis then you just have an old controller and need to stop b**ching, it's just a controller, its weight has nothing to do with your skill level.
The playstation hardware has everything needed if someone wants to setup a console as a media center. Streaming media onto your PS3 usually doesn't even require transcoding, PS3 Media Server is a java based (i.e. it works on every OS) app that allows you to transmux(this is not the same as transcoding) videos into a format suitable for PS3. Xbox has no wifi, HD-DVD is a failed format, and the media center extender thing just plain sucks.
If you get the newer PS3s then you get full PS2 and PS1 compatibility, if not, you get at least PS1 compatibility. Xbox has a limited amount of games that are backwards compatible, a decent sized list but still not even close to the full game library.
The PS3 has a better interface IMO, it is clean and I can have a nice fullscreen wallpaper, and if I want, I can skin the icons. The NXE is huge, full of ads and useless junk, and has a giant silver somethingorother hiding your wallpaper. PS3 wins on interface, no doubt.
The PS3 has a web browser, it is really slow, but at least it is there and requires no workarounds. It even supports flash so you can watch youtube. The xbox has a limited online component, the netflix thing is nice but the PSN store allows you to rent movies as well, just at a pay-per-download kind of thing rather than a monthly subscription to netflix. I'm sure the netflix video library is bigger but the PSN store movie library is quite impressive.
Sony is stingy with their controller technology so games like Rock Band and Guitar Hero have to still use a USB adapter to support the third-party controllers. As a result, the RB and GH controllers are not usable on the opposite game. Any guitar will work on either game with the 360.
The playstation allows Linux, which really isn't a plus since Linux runs like molasses on it but at least it has room for experimentation. About the only "hacks" readily available (i.e. without console mods) for the xbox are done by modifying the media center.