Li-ion batteries are very common in high-drain technology devices. They're commonly used in mobiles, laptops, mp3 players; all sorts.
They are different from other rechargeable batteries like Ni-MH and NiCad because they don't suffer the memory effect. I.e. you don't have to make sure they're fully discharged before recharging to maintain their capacity. Speaking of which, they tend to be of much higher capacity in terms of size/charge held compared to those battery types. Their major downsides are price and heat sensitivity. If they are exposed to heat for long periods, this can reduce their operational life and capacity capacity.