I use RSSOwl too, but I recently switched over to the RSSOwlnix fork of this open source project. RSSOwl is built on an older version of Java and does not support TLS-encrypted sites, so more-and-more RSS sources are incompatible with RSSOwl (for example, Bloomberg recently updated their servers to use TLS). RSSOwlnix remedies this.
I know you said "windows", but Linux users should also be aware that RSSOwl has several known security vulnerabilities.