Servlet filters have been around for awhile but each time I use them I'm impressed with what they accomplish. In dW they're especially useful when we integrate an application into our environment.
In mydW filters are firing all over the place. They prime your profile
information from our IBM registration system, make sure you go where
you want to go when you login, log you out etc etc. We could have gone
and made these changes but then we'd have to repeat them with every new
release; we'd essentially own some of the base product code, a
situation you want to avoid if at all possible. By using filters our
changes are elegantly placed on top of the base product and can be
easily migrated to a new release.