So FeedDemon isn't quite the savior of RSS aggregation for me under Windows XP, but I've configured it well enough that the actual task of reading doesn't drive me up a wall. Now if I can get some semblance of the hierarchical outline that NetNewsWire has I'll be happy.
The key thing about NetNewsWire's outline and how it presents folders is that it provides so much context on progress made. I can quickly see how many unviewed items in aggregate are left, as well as in particular groupings.
You really don't appreciate some things until they're gone.