Hey Matt,
For now, we've kept the existing matchers working with both Rails 2.3
and Rails 3. There were a few matchers that had to change drastically
(filter_params, for example). In those cases, we've added conditional
logic in the matchers where appropriate. We even have two rails roots
in the shoulda test suite for now.
I'd be more open to having new matchers that only work with Rails 3,
since people aren't already depending on them in their existing test
suites. They'd only have to upgrade if they wanted the latest and
greatest.
-Joe