So far we've used dwarven paragon class and the dragon totem variant barbarian (though we only use the mechanics, not the actual dragon totem). Both are being used by the same character. He's only been around for several sessions and will be retiring in a few more, so it's hard to say how well they've worked -- okay, I guess. The character is being retired because the player is leaving the campaign, not because of any problems with these rules.
Overall, I wouldn't say that Unearthed Arcana excites me too much. There's some good stuff in it, but a lot of what's there seemed to be done better in other d20 games. In particular, the class armor bonuses and the damage save mechanics both felt sloppily implemented to me, though I have to admit that I did not try them out in play.