It looks like someone is finally doing a commercial R of some sort (and congrats on the series A to anyone who may work there) over at REvolution Computing (and thanks to Ben for sending me Google alert). I always sort of wondered why Insightful didn't try to wire up their GUI stuff from S-PLUS to the R engine, aside from maybe some sort of licensing concern. Though it looks like a lot of people involved are ex-Insightful the website seems to indicate more of a focus on support rather than front end--I'll be very curious to see how that plays out.
No official Mac support though, so it's unlikely to affect my life for the time being. ;-)