Here's Disney's press release.
More details in a hollywoodreporter.com article.
Comicbookresources.com has more answers.
And Marvel editor-in-chief (and AWESOME artist) Joe Quesada telling fans not to panic. He also goes on to say, "If you're familiar with the Disney/Pixar relationship, then you'll understand why this is a new dawn for Marvel and the comics industry."
I have no emotional attachment to any of Marvel's 5000 characters, so I'm not overly concerned about what the House of Mouse might do with the heroes and heroines of mighty Marvel. Joe says that they're excited at Marvel, and I think they should be. If you want to expand your brand in entertainment, Disney would definitely be a brand you want to partner with. Especially when they buy you for 4 BILLION dollars!!!