By the judgement of developers, ZFS is no longer considered experimental in FreeBSD :)
Thanks to everyone involved, especially Pawel :)
ZFS has originally been imported just before 7.0 was released and it had lots of work done on it since then to make it stable enough for general use. It looks as it's finally payed off and there are no more known issues that would make it not recommended for general usage.
This "nonexperimental" version of ZFS will be shipped with FreeBSD 8.0, expected in the following weeks and it will very probably also be included with 7.3, due to be released sometime around New Year (I'm guessing).