I'm still running Yukons with Super joints & 37" tires and the are living fine so far. With that said they should break in the driveway tomorrow. %)
Here's a thread on Pirate about the RCV axles -
http://www.pirate4x4.com/forum/showthread.php?t=855207
Looks like a couple guys have broken them and it seems RCV honors the warranty. Looks like one guy had an issue but maybe it was a mutual issue.
IF they are as strong as they say it may be worth the money. I have only broken one axle shaft and it was stock. I don't use alot of skinny pedal but that could change.
I might look a little closer at these WHEN my axles go.