If you’re following the Ferret mailing list this is old news for you, as the release took place a week ago or so. For the sake of completeness, here’s the official announcement: acts_as_ferret 0.3.0 has been released!
acts_as_ferret now supports the Ferret 0.10.x series. Due to API changes in Ferret (it’s much cleaner and more Ruby-like now) acts_as_ferret 0.3.0 and up won’t work with Ferret versions before 0.10.0 at all. Ferret 0.10.4 is highly recommended.