One of the neat new (though understated) features of Lion is Whole Disk Encryption. Before I flick the switch, I'd love to know what the performance impacts (speed and battery impacts) of switching it on.
There are some great articles with qualitative data (see below - not to mention a good Ask Different Question), however it would be great to have some quantitative (or even anecdotal) stories of people who Filevault 2 has, or hasn't worked for.
What implications have you experienced in speed and battery life using Filevault 2?
Using FileVault 2: Performance impacts Once you have Filevault 2 enabled, you will not notice any performance changes. Whether it is real or a matter of perception, your files feel like they open just as fast. Your apps launch without any additional delay. Your backups via Time Machine work the same, etc. (themaclawyer.com)
All forms of whole disk encryption benefit from the current imbalance between CPU power and disk speed. In almost all circumstances, the CPU in your Mac spends most of its time twiddling its thumbs with nothing to do. This is especially true for operations that involve a lot of disk access.
Whole disk encryption takes advantage of this nearly omnipresent CPU cycle glut to sneak in the tiny chunks of work it requires to encrypt and decrypt data from the disk. Apple also leverages the special-purpose AES instructions and hardware on Intel's newest CPUs, further reducing the CPU overhead. The end result is that regular users will be hard-pressed to notice any reduction in performance with encryption enabled. Based on my experience with the feature in prerelease versions of Lion, I would strongly consider enabling it on any Mac laptop I plan to travel with. (Ars Technica)