Joe Biden is going to campaign in Florida during the GOP convention. I'm going to have to dig up the history, but I believe this is new. The custom as recently as 2004 was for one party to go mostly or entirely dark during their opponent's convention. Or perhaps to run ads but not schedule events. So I think having Biden campaign during this time is fairly new.
I think people have tended to underestimate the degree to which Team Obama has fairly cutthroat campaigners. As a policy negotiator, he's been a total sap at times and/or read the situation poorly, but as a matter of winning elections they don't play with one hand tied behind their back.