In GW4, we have federations (feds) based on time slots. The feds herd users into groups based on the times when they are most likely to be online and able to play a match. I'm a member of the DFA, the Daytime Football Association, since I mainly play during my lunch break.
I don't know if the same model will be used come retail, but anyway, it means that when you log in, you're more likely to be able to find someone else online to play at the same time. We've got 7 feds now in total in GW4, covering from 7am until 3am GMT. The DFA probably covers the widest slot, from 7am till 4pm GMT, and is ideal for people who work shifts, or live in the far east.
The DFA currently has 51 members, so I arranged it into two divisions - the Premiership has 22 teams, the Championship 29. This season's Premiership race is incredibly close, with James' Kaswell side and Koh's Kampung FC probably edging out as favourites. The division is so close that we can all take points off each other, and anything could happen. I have a good chance of repeating last season's 5th place.
At the end of the season, 3 teams will be relegated to the Championship. Teams that have been inactive - I'll post more on that soon - will be relegated, removed from the fed, or deactivated from the beta, depending on the severity of their inactivity. The DFA Premiership is really active this season, so the teams that get relegated will be decided on merit (or lack of it!).
Ideally, i would like 3 or 4 divisions of 22 in the DFA, though I would always restrict things so that no-one was ever more than 2 divisions away from the top flight. I decided to merge our Championship and League 1 this season due to the odd number of members - a bigger division means more games, and more chance of finding someone online too. We were lucky to poach a number of good sides from other federations this season as well, which helped a lot!
The other role of the feds is financial - the fed makes a daily payment to all members, the size of which is determined by the reputation of the teams, essentially. Also, the competitons offer cash payouts - so fed income probably equates to 20-30% of a team's income - a really important amount of revenue.
The feds are all unique as well, so the different organisers implement different league structures and payout systems. There are youth leagues and cups as well - From the Casual to the Extreme, FML offers everything you could want for you to get as involved as you wish to.