Game console dilemma - Xbox 360 or Sony Playstation 3

I've been recently going down the path of re-shuffling my home media environment. Since I'm also still kicking the tires on various PC games (the new Steam community site is very interesting (link is my userid, you may need to be logged in) -- for the record, all the other games I mentioned I'm no longer playing.

Anyway, I've been thinking about a game console at home. The choice is really between the Xbox 360 and the PS3: the Nintendo Wii is a great supplementary machine with its very different interface options and social nature, but not such a great media center. I'm more likely to buy my own Wii controller and go over to friends that already have one.

Both the Xbox 360 and PS3 seem to have solutions in place to easily share media from your Mac. There is Nullriver's Connect360 and there is the open source MediaTomb which can let you run an open source UPnP server to share to both platforms (older how-to).

The Xbox LIVE and Xbox Live Arcade is compelling. Easily download small mini games. Get an account, earn achievements. Even playing "simple" games, you can compete with other people at home anywhere else online with you, and "invest" in an identity.

But...

...it's Microsoft. I acknowledge they've built a very interesting machine. It's much more of a market win than the PS3 by a long shot (at this stage of the game...). But it's optimized to work with Windows Media Center, and it's not really that hackable.

The PS3 on the other, I love for its open-ness. It actually has "install other operating system" as a *menu item*. That's fantastic, and totally appeals to me wanting to tinker.

But...

...for the price of a PS3, I could buy both an Xbox 360 *and* a Wii. It's pricey. Am I buying into tomorrow's technology, today? Also...it does come down to the games. And to the social network. My social network mainly has Xbox 360s (aside from Mark Yuasa who has a PS3 in addition), and some of the upcoming games that I'm interested in (e.g. Mass Effect) are Xbox only.

Hmmm...it seems like in writing this, I've convinced myself. My heart says I should get a PS3, but my head says Xbox 360.

What would you get? Why? Do you have one already? What do you use it for?