[bodywerks]

More importantly than a shortened life is the voided warranty when running unregulated li-ions or lipos.
Best setup, IMO, is dual A123's. They are extremely robust and have a higher C rating than even the best lipos. Also, a 2S pack has a nominal voltage around 6.6, so no regulators are needed. You do typically need an A123-capable charger, though, unless you go with the new Duralites. They are about the most expensive and are slightly heavier, but they have built in circuitry that allows you to use your li-ion/lipo charger.
Depending on your stance about field charging, you will need to choose the capacity accordingly. The advantage to the A123's is that they can push serious amps, while also maintaining good voltage, so you could technically run a single 2300mah pack on a 40%er. For redundancy's sake, I run dual A123 2300's on planes 100cc and up, and dual 1100's on 50cc and up. Below is a 42% qb 260 that I am running dual self-made A123 2300's. I burn 450-500mah per flight. so I am goof for 6-8 flights on a charge, although I just keep my batteries topped off all the time by field-charging.