Facets 2.9 is fairly extensive as it was originally intended to be v3.0. After further consideration it was decided to reserve v3.0 for something a little bolder (to be announced). The primary goal of this release was to trim Facets down to a true core extensions library. All tertiary add-on classes and mixins have now been spun-off to other projects. Only a very select set of general purposes classes and mixins remain.
A new TOUR library division has been added to complement CORE and MORE. This division houses purely optional extensions. The new division serves a couple of useful purposes. In particular, it helps separates the standard library extensions from optional core extension in the RDocs and thus makes the perfect place to vet new extension ideas.
One important change that will effect anyone using Facets along side ActiveSupport is that Facets no longer tries to conditionally avoid method overlaps with ActiveSupport. This is fine for the upcoming ActiveSupport 3.0 library which extends core classes directly instead of using mixins. One need only require 'facets' in Rails' config/preinitializer.rb file, and ActiveSupport will take precedence over Facets. For older versions of ActiveSupport, the best approach is to cherry pick from Facets just the extensions you want, thus avoiding any conflicts. There are actually only a dozen or so overlaps and all are intended to compatible, but it doesn't hurt to be sure.
I won't detail each change here, have a look at the HISTORY.rdoc file for that. Needless to say, it's a good idea to read it over to see what changes might effect your usage --and it also gives you a glimpse at what other extensions are available that you might not yet be familiar.