+1 on the LiFe batteries. They are well worth their money. One thing to watch out for is the extra voltage - receiver and servos need to be rated for this, or you might burn them up sooner or later.
Most newer systems can handle the voltage, for everything else you can use a voltage regulator.
Yeah, some people just hook it up and 'never had any problems', under high load conditions you might loose a plane, not worth the risk.