It is unfortunate, but the OpenBSD disk encryption tool-sets are no where near as mature as those found in FreeBSD or Linux. You would think with such a security focused operating system that disk encryption would be a no brainer. You would be wrong. On OpenBSD -misc mailing list you often get this impression with them: XKCD - Security ...
Wanted to share a quick “how does it work” about PGP WDE for Mac. http://www.pgp.com/mac/ This is the only solution that does pre-boot and true WDE for the Mac. The software is 189 for a yearly license or 239 for perpetual. The software itself is very “apple-ish” with great wizards and walk through for those not familiar with key based authentication and encryption. Some of the features are: WDE for Intel based Mac running 10.4/10.5, no SL due to the 64bit kernel from the debug trace on my Mac Pro :) ...