The "dual class characters" update posted to the WotC website today, and it is interesting. At first, it reminded me of 1st/2nd edition multiclassing, in which your character got the average hit points of your classes, but that isn't a fair comparison because you don't get stuck with a slower progression rate and you don't get all of the abilities of each class.
The system appears to be a lot cleaner than I'd expected. Basically, you just cut two classes in half (rounding down on everything) and add the results together. Fighters get 15 hp to start? Well, half of that rounded down is seven. Rogues get 12 hp to start? Half of that is 6. Therefore, a 1st level Fighter/Rogue will get 7+6=13 hp. You have 2 at-will powers, so half will be from Fighter and half will be from Rogue. Powers don't have to stay half and half throughout your career, though; you just have to have one from each class in each category (at will, encounter, daily, utility) at all times.
As far as class features, it appears that you get only the most important one(s) for each class to function, and the ones you get are preemptively nerfed so as not to be too easily abused. For example, the rogue can still sneak attack all he wants, but he can only do it with rogue powers, and he doesn't get the benefits of any other rogue class features. There is a workaround for the lack of class features, though. There's a nifty little catch-all feat in the article that basically says "Choose a class feature from one of your hybrid classes. You get it!"
My initial thoughts are that my group will largely ignore these rules. I'm the only one who runs multiclass characters. However, I really like the rules. Although my opinion may change once I actually use them, the rules appear simple and clear-cut, and because my characters will get less abilities that I constantly forget to use (like Prime Shot), I've got a feeling that my character sheets will actually feel less cluttered than they do now.
This may be the multiclassing fix/replacement that folks on the WotC message boards have been begging for. If the community response is as positive as mine, WotC may have satisfied a fairly large group of "4e multiclassing sucks!" complaints.