I just downloaded the latest release of Resin. They are not for anyone with high blood pressure. On the other hand, the two features in the new snapshot may be very nice from a development standpoint. The plugins now automatically detect changes in resin.conf so you don't need to restart IIS or Apache just because you added a servlet-mapping. They check every 15 seconds.
Sessions can now persist in files.
This is useful during development, so your session won't disappear just because you changed your servlet. Having to login after changing a file was driving me nuts. The implementation and configuration will change, but this is a first cut. This is, of course, useless for distributed sessions.