FileVault Performance Compromise? I'm thinking of using FileVault to secure my computer - it looks like an ideal solution for everything. However, I'm wondering - will it effect the performance / battery life of my computer significantly?

I've got a 2010 MBP with 8gb RAM and a 500gb WD HDD, and the battery at the moment is good for about six hours. I'm running OSX10.7.1.
I can't comment on how Lion's FileVault 2 affects battery life, but I've had it running (Full Disk Encryption) on an older (2007) MacMini with 3GB of RAM for a few months, and it is a great solution for keeping a computer that might get stolen secure.

Beyond the initial encryption, which took a few hours, I really haven't noticed any performance difference. Given that this is an older machine, any negligible difference I might have missed would be even smaller on a newer machine like yours.

I was curious about this myself at the time and found this AnandTech article, which boils it down to a negligible CPU load, and a slight hit to your hard drive's throughput. They were using an SDD though, so the results may not exactly correspond with a spinning disk.

So if you're reading and writing to the disk a lot, you might notice a slight decrease in battery life as reads and writes will take a bit longer, but I doubt it'd be anything too drastic.