PGP Whole Disk Encryption (10.0.1) does now work on Snow Leopard (10.6.3), and it seems to work well. On my MacBook Pro, there is no noticeable reduction in overall system performance with PGP WDE, except that the boot process takes about 15 seconds longer than usual.
I can recommend PGP Whole Disk Encryption, but for email encryption I find PGP's commercial product a bit klunky (it's proxy-based so it doesn't integrate with Mail.app in any way). For PGP email, I use Thunderbird + its EnigMail PGP plugin, which seems smooth so far, even though it meant ditching Apple's Mail.app. Fortunately Thunderbird 3.0 is polished, and integrates with Address Book and Spotlight.
I would argue against using Apple's FileVault to provide filesystem security. Firstly of course it's less secure (it can't protect the operating system binaries and config files from tampering - it only protects your user files). Secondly I've tried FileVault on my home directory in the past, and it was noticeably slower at starting up and especially at shutting down. If you want encryption, I think it's faster and smoother to encrypt the filesystem rather than using an encrypted file container.