I have used the demo of Joomunity on their site. Still very buggy, but what would you expect from something in pre-alpha.
From what I can see the layout of profiles in Joomunity is much cleaner and is more what is expected in profiles now with the success of Facebook.
From what I can see the functionality will be very similar, but with Community Builder you have years of development which one could only imagine goes along way.
But as I said, the interface is very very slick in Joomunity and for one I hope that the Community Builder guys take a few notes from them on this side of things.
Will be interesting to watch and I wish both packages well. They both do amazing things for Joomla and it's community.