Square Enix just released some more information about the Final Fantasy XIV game system. One of the interesting aspects of it is what they call the "Armoury System." The idea behind it is your skills are determined by what you wear. Arm a sword and you can be a warrior, pick up a staff, and you can be a mage. And you can change at almost any time!
And this is a good thing, in my opinion. I like job systems much better than the traditional static class system where to experience different jobs you have to grow a stable of alts. One of the main reasons for this is: I hate doing the same quests over and over again for each alt I raise. I hate having to grab the same flags (for fast travel or access quests) over and over and over again.
It's also easier to change what you are doing based on role - if I join a group and the roles we need change, and I can satisfy that, it's nice to know I can instantly swap out for the needed role instead of logging in an alt and dragging them halfway across the world, hoping they have all the right flags and access quests done.
It also helps with the community: in Final Fantasy XI, I might go out and see a Samurai is looking for group. However, I then realize this is the same guy, a good player, who was healing me the other day. So I know he'll probably be a good player in his new role. In EverQuest II, I almost never know who I'm getting involved with unless it's a guild group, since everyone in game has at least a half dozen different names and appearances.
It looks like the job system is become much more prevalent. Heroes of Telara mentions the ability to change subclasses at any time. Free Realms implements a job system as well, letting you swap jobs almost anywhere. The Agency likewise will allow you to swap between roles based on what you wear. This mechanic seems like it may be a defining trait for so-called "third-generation" MMORPGs.