My personal experience...
I just bought a complete Bianchi Infinito w/ full Ultegra 6700. I thought about running it for a few weeks on the bike before swapping it out for the [mostly] Centaur stuff I already had on another bike.
I rode the bike up and down the block a few times (maybe a total of 1/2 mile) before I had enough and pretty much immediatly put the Campy on.
I have nothing against Shimano, IMO there's some things about the new stuff that really is nice, and I've actually had chances to ride the 6700 stuff on "proper" rides previously. But at the end of the day the Campy stuff just has a special character to it. Maybe if I didn't already have Campy I'd like Shimano a lot more; hard to explain, but Campy is one of those things where "once you get it, you 'get it.'"
The Shimano stuff worked fine, but there was just that something special missing. Best way I can describe the new Shimano stuff (Ultegra and by extension 105) is that it's like having Campag Centaur without its soul. (Again, just the way I feel)
(p.s. my Centuar stuff consists of pre-07 carbon crank & skeleton brakes, w/ Centaur UltraShift levers in alloy; RD is Athena, FD is Veloce; and yes, the Escape Mechanism stuff did suck.)