Three nights out of an in-game month really aren't that many. Plus, it all depends on when, in-game, the GM's game takes place. Obviously, the GM will have to keep track, but that's a minor detail.
As for it being trouble for the other party members, look at just how early in Harry's career he encountered his first loup-garou. Fairly early. He was still wet behind the ears, despite his past. If you look at Fool Moon as a gaming session, the GM running it was rather sadistic.
I'm in a group that puts value into player character back stories, and personal conflicts inherent to each character. We like exploring the good stuff as well as the bad stuff about our particular characters. I tried running a Dresden game using GURPS and only got a few sessions in before our wizard pc flaked and left the group. The person that played the loup-garou cursed guy in my game wants to play him again when our new Dresden game (not run by me) starts.
Also, it's not like every person with the curse would have the exact same one that plagued MacFinn's line. Some might have the chance to become free of it, thus becoming pure mortal (similar to White Court Virgins and Changelings). The way I had determined how the pc in my Dresden game was cursed was that his curse would end once he learned to control the beast. In the Dresden RPG, a character like this would hit a milestone if he comes across some hint as to how to control the beast.
The two ideas I have for my own characters in the upcoming campaign are nowhere near this complicated, since they'll be pure mortals. Clued-in, but pure mortal nonetheless. Which is odd for me, since I love Dresden and the other characters with powers, and even played a mage (who was a PI and insisted people refer to him as a wizard) in our old World of Darkness game run by the same guy that's going to run Dresden. But I firmly believe that our loup-cursed wannabe should be able to play his character without being penalized by taking powers he can't used. A high aspect and trouble should suffice.