For details, you should check out the electric forums.

Lipos are a bit more expensive, and you MUST HAVE a charger designed for them. If you use a Nicad charger on Lipos, you can damage the pack, or even have it catch fire. The cells are "safe" if used correctly, but can't be abused the way we tend to abuse nicads and nimh cells.

But the capacity for a given weight is amazing.