What are the implications in speed and battery life while using Filevault 2?
Other than making sure you have power available when you turn on or off the entire disk's worth of IO to encrypt/decrypt, performance and power deltas are barely measurable.

Less than 1-2% is what I'm seeing. Other than hammering large IO benchmarks, in practice it doesn't matter one bit whether FileVault 2 is on or off for the initial build of Lion.

As long as you understand the limitations of not being able to use file recovery tools, how people can circumvent your encryption by losing control of pass phrases or keys, it seems this lunch is free (or at least on Apple's tab).