There was a game called Legends of Kesmai by Kesmai Studio\'s played on AOL and Gamestorm that had a skills system that allowed skills in a direction that was inline with with thier classes.  

To advance at a fair rate and would softcap other skills at a low level like skill level 6 or something ... then they would have to train skills that were not inline with thier classes much more to gain levels.  Each level was twice as hard as the last level so you could hit lvl 3 in a day to lvl 6 might take a week 9 in maybe 2 weeks and 12 in a month.. to 15 might take 4 months and 17 in maybe 6 and 18 maybe 9 and 19 after maybe a year ... nobody ever hit 20.

I had a wizard that was a 19th lvl with 17 lvl magic .. that was pretty damn good but I also had lvl 14 Martial artists which was HARD AS HELL to get and it took me about a year... it was a great system that not only involved using the skilll VS MOBS but you also had to use currency to train with a trainer to be able to promote the class skill faster.

Now that I think about it I think they regulated it by not allowing non aligned classes to train skills after a certain level.

EDIT: PS yes a jack of all trades and master of none is true... but pretty much nothing survived a DragonKick followed by a lvl 17 IceSpear.