I was wondering about this as well, but I'm currently playing a level 5 Barbarian/level 1 Rogue and he is not only fun to play, but also very capable in many respects.
I'm going down the elemental rage path, which adds to damage a bit and intimidating glare is very fun because you can intimidate people as a move action. Plus, since he has the thug trait as a rogue, his intimidating glares can actually frighten people at times.
I want to get the knockback rage power along with strength surge for some battlefield control.
Overall, I think the only challenge will be keeping the damage output up at the higher levels. But the fact that my Barbarian can stealth quite well and do some sneak attack damage gives him a bit of an edge.