Who chooses Intel? Mainly mobile users (Centrino, but Turion is still better), and ignorant customers (ie, people who buy from Dell).
AMD outsold Intel this year in processors in the OEM and retail market, so clearly, AMD is doing SOMETHING right. Don't forget, AMD has its memory controller on die, which means it doesn't have to move information 1-3 inches and back to be fully processed, just a few nanometers. Also, the memory controller for Intel depends on the motherboard's northbridge, so if you got a cheap motherboard, you got a cheap memory controller. Then you got crappy performance.
AMD is cheaper, faster, and overall better. To those who said media and graphical art users are those who use pentiums, you're dead wrong. Many of those people in those fields either use Mac's or processors which belong to the Athlon 64 FX line of processors.
Trust me, I've been using Intel up to a few months ago, and when I made the switch, I've never been happier. I'm running an Athlon 64 3000+ Venice core. It's "clock speed" is 1.8ghz however it is equivalent to a 3.0GHz Pentium, and truth is, it runs faster then any pentium on most of the games I play, did I mention I haven't overclocked it yet?
I could go on, but main selling points are it runs cooler, 64 and 32 bit, cheaper, faster, and a better overclocker.