Some more things to know about swapping to Lipo packs:

They can supply WAY more current with less voltage sag than NiMH or even A123 packs, so you might find your ESCs or motors get hotter than before. Batteries used to be the weak link in the system but now they will happily fry your other components if they are under spec for the job.

Lipo packs do not like to be fully discharged and most people recommend leaving 20% charge in them. Fully discharging them can damage cells and in extreme cases, cause a fire.

Use the space and weight saving to add shock protection around the Lipo packs. The foam in exercise mats does a good job.

Using high discharge packs is a smart idea, even if you don't need the current rating. High current packs in the 50C to 65C range have lower internal resistance and don't get as hot. This means they can be recharged sooner (its dangerous to recharge Lipo when hot) and you can usually charge them at higher current. My 4.25AH packs are OK to recharge at 8C, which is 34 amps, very handy when you have back-to-back finals matches.

While everyone loves their Optipower packs, I have been very happy with my Turnigy nano-tech A-SPEC packs. They have performed flawlessly for the last two years and while they might not be quite as good as name brand packs, they are much cheaper.