I've updated my FreeBSD system with "freebsd-update" but "uname -a" still sais it runs the ""FreeBSD 8.1-RELEASE #0" kernel.
How do I get #1? Its important because I need ZFS v15.
Your upgrade worked just fine. The #0 will not change after an update but the -pX will change.
If you want to upgrade your ZFS version don't forget to run
zpool upgrade after freebsd-update.
Please note that currently v14 is included in the 8.1-RELEASE version.
EDIT: Sorry, I didn't read your last comment. Please check out this link and switch to CURRENT branch: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/current-stable.html
The problem was, that the install image of my root server provider was patched with a ZFS v15 patch, but the rescue system is not.