Updated mechanics for hybrid characters is out, marking the end of May's issue of Dragon. It is complimented by a Design & Development article, giving you some insight into the designer's thought processes and methods.
The two big things that I noticed are that hit points and healing surges are now given in fractions, so you no longer round down and miss out, and the Hybrid Talent feat lets you pick from a list of options that are detailed in each hybrid class. Some of them work as explained in the class, while others are a bit different. You can also use it to become proficient with all armor and shields that the class might provide.
Note: Oh, you can also use paragon multiclassing to steal more shit from one of your hybrid classes, like how you can use paragon multiclassing to boost your multiclass-class.
At some point today I'll build a hybrid character and compare it to a single-classed version to see how the math holds out (probably a druid-shaman). I like the theory of having a character that is a bit more evenly spread out, but I dont want to gimp myself for the sake of the concept. Only a handful of classes ever benefited from multiclassing in 3rd Edition, and those were the classes that werent getting anything useful anyway.
Multiclassing as it exists now lets me supplement myself and enforce the concept with the price of a single feat, and its cost I'm willing to pay since I know that despite everything else the rest of the character works fine (and I basically got Skill Training with something extra).