I've got a Campagnolo Chorus 2x9 drivetrain on my bike. Lately I've found that shifting to the big ring is very difficult: The only way to get it to shift at all is to make a simultaneous front and rear shift going little>big and big>little; I assume that this introduces slack into the chain to make the shift easier. This isn't always successful, and when it is, I wind up overshifting (which is easy enough to correct, happily).
It hasn't always been like this. Not sure where to begin diagnosing the problem.