A large part of it is, of course, kept by the poker room, which will partly re-invest it into things like print and TV advertisements. Through these, it tries to attract e.g. hobby players that deposit money once in a while in order to play for fun. After all, the winnings have to come from somewhere; mostly from the "fish" that are attracted with advertisement financed by your rake.
The part of it that goes to PokerStrategy.com is for the most part directly re-invested into the maintenance and improvement of our strategy offerings. Just take a look around and you will quickly notice how there is something happening and changing everywhere. New videos on a daily basis, new articles, daily live coachings, more employees to improve the support...
Your rake is therefore directly reinvested for your own benefit and the benefit of the other members. A cycle that benefits everyone, especially you as a player.