In particular, Disney will be absorbing a 30% ownership stake in Hulu, giving them considerable say in what direction the site takes. They will be joining NBC and News Corp, who are the current owners. In return for their contribution, Hulu will receive a significant amount of additional content from Disney's library, adding dozens of new shows to their growing list of ad-supported videos. It isn't mentioned whether or not Disney will be providing content in HD quality, like some Hulu content already is.
The site still has a lot of growing pains to get over, ranging from content organization to video selection. They also have a few PR issues to tackle, as they aren't always very friendly to third parties that want to build off their service. Aside from that, they certainly have enough big names backing them at this point. The only major provider left to grab is CBS, though they have burned a bridge or two with them already. Can they turn that around?