There are a number of live applications running on Catalyst. Some of them are listed below. Many other Catalyst-based applications are in production but internal. See http://www.catalystsites.org for another list with screenshots for each app. See also Perl 5 powering Web 2.0.
For tips and tricks from behind the scenes of the iusethis development check out Marcus' Bag of Tricks from IUseThis talk.