Hi y´all !
Well this is a big disadvantage for duaing and multicass fighters. Well I think you all are going to love the 3:ed rules since in t you get all benefits from each class, there is no Kits available but after awhile you meet the requirements for a prestige class which will allow you to be either an assasin, fallen Paladin r an bow expert and so on. You cannot be a multiclass in the 2:ed way though you can dual from start so to speak and you can have as many dualclass as you whish but you will have a heck progressing to thoose high levels. So far there are no rules for characters to go beyond lvl 20. but hopefully there will be. More cool stuff is that most characters aren´t restricted to anything, you have some things you cann0t do but otherwise it will only cost you some harearned points and you can have a mage with a twohanded sword wearing a studded leather armour, though he will have something called spellfilure if wearing armour.
Check it out further at
http://www.wizards.com there are some cool articles there and feel free to ask, I bought the rules to see what hppened and I have played some too but mostly I´m the Dm..