Something's gotta be running heavily during that time. Download Spare Parts from the market and use it to see what's been running.
I'm guessing you're not getting very good battery life?
Also, how's your awake time? Menu > Settings > About Phone > Status
Downloaded Spare Parts, doesn't tell me much really. Battery life not very good is an understatement. Battery life hits 70ish% after 2 hours, and thats me not even using it.
I downloaded the Handcent, I like that program, but for some reason, my default messagae still pops up the notifications, and I cannot figure out how to stop it from running at all, so thats bugging me.
I have bluetooth, wifi, gps, network, all turned off, still crappy battery life.
Love hate relationship right now, I love the Hero, its my fir android phone, I freaking hate the battery life. My old Razr 2 had crappy battery life, and I was at least expecting the Hero to be slightly better, 6-9 hours of useage time is not really ideal for myself and my job.
I don't even listen to Slacker radio or pandora no more, because I can't risk it dying on me. Weak man.
Oscar