Currently, most of my sensitive data is encrypted via encrypted sparse images, but I find managing encrypted volumes to be a pain in the butt (mount, unmount, mount, unmount). I recently purchased PGP Desktop for Mac, which (finally) features pre-boot whole disk encryption. I love the idea that my drive(s) would be encrypted, and that a password would be required even before boot, but I wasn't sure what kind of performance hit I'd get if I used PGP on an entire volume. And so, I ran some benchmarks.
The results aren't pretty. I ran the benchmarks on a solid state drive hooked up through an SATA->IDE bridge (I know -- I'm sorry. It was the only option, given my setup). At small transfer sizes, the PGP encrypted drive actually performed admirably, especially when compared to an unencrypted spinning drive. But disk performance overall takes a HUGE hit -- in many cases, the drive performed 80% slower when PGP encrypted with default settings.
Assuming the machine was loaded up with enough RAM, I'll bet most people wouldn't even be able to tell the difference when doing normal tasks like emailing and web browsing. Anyone who isn't computer savvy probably wouldn't care, anyway. I find that many casual computer users just accept that computers are slow instead of taking action to rectify the situation (e.g. buying more RAM, taking the CD or DVD out of a Windoze machine, closing some applications).
As a photographer and media-heavy user, I have abandoned all hope of using PGP Whole Disk Encryption on my active OS drives. But I may end up using it on backup drives; portable drives are easier to steal than are notebook computers, and I don't want my backup drives to be an easy way to get data from me.
And now, for the benchmarks: