Two things put me off buying a 360: my severe dislike of the buggy, space-wasting Windows, and all of the reports of errors with the console.
However, over the last year I really got into console gaming (bought a PS3, PS2 and a Wii), and thought that I may as well get the 360 to fill the void. I don't have it connected via HDMI cables or anything as it's in my room, hooked up to only a standard definition tv (my PS3 is the one hooked up to the HDTV in the living room otherwise my Bluray collection is worthless

) so I can't comment on the graphics too much (they still look rather amazing though), but the games I have so far (Fallout 3 and the two Gears of War games) have been consistently enjoyable, moreso than my PS3 games (I disagree with people that say MGS4 is one of the best games ever made, it's a bloated mess with almost no gameplay in comparison to the movie-length cutscenes).
I got my 360 on November 19 - the same day that the New Xbox Experience was released (although I didn't know this, and was totally surprised when it updated). I only used the old software for a couple hours and I wasn't very impressed, but the NXE just blew me away.
Overall, I still prefer my PS3, mainly for the Bluray playback and the fact it is the console I have some of my favourite games on (mainly GTA IV, COD4 and Guitar Hero World Tour) although it does have some I don't like (MGS4...); another thing I like is how I can copy videos to my hard drive, as opposed to only being able to copy music to the 360. But this is a very, very slight difference; even if the PS3 is still my favourite, the 360 is only just behind.