I feel like I should work on FeedReactor, but I started work on that to scratch an itch and exercise my RSS, Atom, and Ajax skills. But, lately, I've been made reasonably happy and itch-scratched by the latest betas of NetNewsWire, and my RSS/Atom skills are getting quite exercised by writing a book.
Furthermore, I had brief, weak delusions of toppling the Bloglines empire, but I'm not really devoted to that idea as a venture of my own. Been there before (sorta), never got anywhere, left a domain name and two dead-and-deleted SourceForge projects behind me. (And, a project really has to be dead for SourceForge to delete it.)
Though, if someone else wants to hire me to build it for them, I don't think I'd turn down the offer.