Re:
They make a difference to your top tube if they turn around too far!
I like the idea in principle but have a pair of Scott AT2's on one of my bikes to avoid the above problem. They're built in, so no chance of damage to the frame.
I like using them , both off-road on the flat and climbs. Also great on the road, as I'm more streched out than I would be.
However, i do think they don't look as good on a bike as just a pair of flat bars, but that's just my personal preference
Mike