I'm in seven this year myself. Two are buy-ins and five aren't. I'm in the semis in all five non buy-in leagues, and didn't make the playoffs in the two buy-ins, haha. I'm thinking about writing a book called "How to Win at Fantasy Football and Still Lose Money."
But for the record, one of the buy-ins is an auction league, and the other has a bunch of crazy rules. Only five bench spots, position limit of 5 on RB's and WR's (those aren't too crazy), and then it uses FAAB, but the really crazy rule is that there is no waiver period. You have to wait until the next day to pick up a player regardless of the day, meaning that you have to use part of your FAAB every single time you pick up a player, and if it's Sunday morning after 11am, you can't pick anyone up for that day's games. So if two of your WR's are on bye, and you only had two others on your roster, and one of them gets injured, then you're stuck. Also, it takes 3 days for a trade to clear, so if you trade on Thursday night, it won't actually go through until after that weekend's games are complete. So anyways, definitely not doing that league again next year unless some changes are made.