I'm not an Xbox fanboy or anything, but the 360 is my sole game console this generation.
Why did I buy it? Because the PS3 was a mess at launch. The PS2 was my sole console during the previous generation and I had assumed I'd be purchasing a PS3 when the time came, but the PS3 was really expensive and just didn't appear to be worth the money at the time. When it finally launched here in Ireland it was four months late, lacked backwards compatibility, and was an obscene €630. Yes, it had a blu-ray player in it, but that wasn't much of a selling point considering all I had at the time was an SDTV. By trading in my old PS2 and a few games, I managed to get a 20GB 360 for €200 in early 2007.
Early on in the 360's life, it had a lot of great exclusives like Saints Row, Crackdown, Viva Piņata, and Mass Effect, and MS money-hatted a number of timed-exclusives as well, such as the GTA4 episodes. I never felt the need to purchase a PS3 because most games I was interested in were multi-platform, and the few Playstation exclusives that did interest me couldn't justify the price of a second console. On top of the great games, I found the controller to be the most comfortable I've ever used.
Around 2010, MS seemed to become complacent and shifted development to focus on the upcoming Kinect, so the core game exclusives dried up. They added services like Netflix and Youtube but put them behind their paywall, which was a douche move. They redesigned the dashboard twice, both times making it slower and increasing ad-space. I still like the console and don't regret buying it, but I do think that PS3 users have had a better experience during the second half of this console generation (not counting the hacking incident).
I completely oppose the DRM that Microsoft is introducing with the Xbox One, but that's only part of the reason why I'm tentatively planning to purchase a PS4 next gen. The truth is that I became somewhat disillusioned with Microsoft over the last few years. At the risk of sounding naive, they don't make me feel valued as a customer, I feel like I'm just a revenue stream to them. I think a lot of people felt the same way I did over the last few years and that this anger towards the Xbox One has deeper roots than Microsoft realises.