So Square Enix decided to make a feature to encourage people to play the various classes available. In Final Fantasy 14 your character has 4 classes he/she can switch between. So if your group needs a melee dps/tank of some sort you can be one, switch to a healer or switch to a trade profession.
It's actually a very good idea. The bad idea comes at forcing people... no punishing people for not playing all 4 classes. SE has created a feature that results in reduced EXP after a certain amount of playtime UNLESS you change classes. This is an example of using the stick and not the carrot to entice your consumers.
It's a horrible idea. Right now if you play over 8 hours in one week your EXP starts to drop for that class. One of my friends said it best, that even if it was 8 hours a day I would feel cheated. I've honestly heard nothing good about Final Fantasy 14 from my friends in the beta. The only positive thing has been "it's Final Fantasy" and I don't know if that is going to be enough.
I was really excited about Final Fantasy 14. I missed the boat on Final Fantasy 11 so I was really excited to play a MMO made by Square Enix. I can't say for sure that I wont buy it, but it is looking more and more like I wont. I have numerous reasons not to buy FF14 and none to buy it.