The battery statistics service tracks number of times acquired, total realtime (aka walltime) held, etc. Here's a sample from a typical bugreport. The user facing UI is, of course, friendlier looking: http://frotz.net/misc/battery-stats-unplugged.txt
It starts with an overview then provides a UID-by-UID and process-by-process breakdown of wakelocks, cpu time, sensor usage, etc.