here is a thread on rcu where they tested all the most common lipoly's
in all the tests they run them down to 3V per cell.
http://www.rcgroups.com/forums/showthread.php?t=342568
ive been running lipoly's since 2002 and have always run them down to 3V per cell on my 3 cell packs and have never had any problems. i use a low voltage warning light set to 9V. my voltage cut off is turned off or at lowest voltage on my ESC's. i dont like the idea of the throttle going to brake/off.
with my moth it runs on 2 cells and the heli will not fly on 6 volts so there is never a chance of going under voltage.
i have packs that are a few yrs old and they still run fine. ive ballooned a few packs charging on the wrong voltage like 2 cells charging on 3 cell voltage.