Another nice thing about T::More is the large number of other helper modules
that play nicely alongside it.
I don't know if they work with T::Unit, maybe they do, but the whole suite is great. T::Exception, T::DatabaseRow, etc etc.
Another link worth posting again is petdance's
testing large projects with perl.
And while I am on my soapbox, let me also praise Test::MockObject.
test driven development -- rah! rah! rah!