I almost guarantee its not the derailleur, its either worn components (cable, housing, chain and chainrings?) or poor adjustment. All a front derailleur does, no matter what level, is mash the chain one way or the other. Its probably the simplest and least sophisticated piece of the drivetrain and the most misunderstood. I have used Deore, XT, LX, XTR, Veloce, Mirage, Centaur, 105, RSX100, Ultegra, 600, Dura-Ace, etc, etc and they all work the same. I can't tell a difference that I can attribute to the derailleur. You'd be surprised how much difference a quality chainring makes in your shifting, and new cables and housing with a proper derailleur setup.
commuter turned bike mechanic turned commuter (also a Velocity USA employee, but this is my personal account)