I used to be a dev who transitioned to a PM and now am the CTO in my own startup. My main reason for becoming a PM was to get more customer contact and be in a position to make customer-focused product decisions. Someone mentioned that PMs make more money than devs, this is incorrect at least in most top tech companies. Compensation bands for PMs and Devs are the same.

Obviously the day-to-day work of a PM is pretty different from that of a dev and the transition is not something that all devs would like or should even aspire to. For those who want to know more about what PMs are supposed to do (and no, it is not just project management :-) check out my blog on this topic - http://avilay.wordpress.com/2013/07/03/what-does-a-pm-do/