I have, though it seems that 800mv is the limit. I have set lower, but it doesn't seem to respect that. On 500MHz if I go below 850mv, I get an instant reboot, if I go to 775 it runs normally. I have been playing with that in mind as of late
Speeking of late. I need to get my wallet from work before I need to be at work
edit: Oh and to answer your questions. I use Incredivolt from the market. And the battery life is maginally improved.