One more thing: Google Reader Synchronization
Any feed that is under synchronization control will synchronize its article read-state, labels and starred state with your Google Reader account.
Another cool advantage of using your Google Reader account for subscriptions is that you will never loose an article from any feed. Just increase the number of articles you want to keep per feed (up to 1000!) and RSSOwl will download them all.
Please refer to our Beta 2.1 Changelog page to find out more and download the beta.