Okay, after playing a G&W that is almost exactly at my skill level, I can say we DEFINITELY have the upper hand, and by a long shot (he eventually had to counterpick Wario... which proved to be a good move, but I digress). Like Gheb said, his trip and get-up animations are soooo easy to abuse, and avoiding his aerial approaches (and shielding the B-Air properly) is very easy to do... if we're on the ground. As far as that goes, I believe now that all of his ground moves are slow, easy to see coming and punish in the post-lag, and can all be punished easily with a Banana throw, save possibly D-Tilt.
I will say when you're above a G&W it's annoying trying to get down when they're U-Airing you (and refreshing their moves... That's just stupid), but pulling Bananas to make him avoid them and Air Dodging at the right time work just fine. The primary problem here is how bad our horizontal aerial momentum is, meaning that credit card will smack you in the face a few times before you make it back down. Playing against G&W turned out to be a lot easier than I imagined O.o
I'm going to reiterate that the G&W is MY skill level... And I just placed in teh moniez in a tournament for the first time yesterday. He knew how to Bucket Brake and do other fancy G&W tricks, so I'm pretty sure he's been to the boards at least a few times. I am basing this post entirely on my experience playing him.
On a completely unrelated note, there are still a LOT of people (around were I am, anyway) who haven't played against Diddy... And that's always lulz (OMG BANANAS WTF SOO BROKEN BAN PLZ)