Hmm.. I'm at 98.33%.
I've completed the story, done all missions for friends, got all the cars for Stevie, did all the assassinations, gotten all the pigeons and stunt jumps, done all random character missions, beat the high score on QUB3D, did both cop requirements, won each mini-game, and I'm pretty sure I've done all the activities I can with friends. Do I have to do every "Boating" and "Heli Ride" scenario for Brucie?
EDIT: Ah, nevermind. Just had to take Jacob to a strip club. Now, if only the Social Club worked right.
I have six days to get my gamercard linked. Funniest thing about all this is that I had no intention of ever going for 100%, but I did so much of it for fun that I was able to get it done in time.