YouTube Partners (online video companies like us and other content owners who have agreements with the company involving shared ad revenue) are already able to upload videos longer than 10 minutes, but it's a fairly big deal for the rest of the ecosystem— and amateur folk make up a huge portion of that ecosystem.
Just think about it: the move would bring 50% more "haul videos," from shopaholic teen girls; 50% more crazytime rants from random dudes; 50% more hamster montages; and 50% more double (whoah that's almost a triple) rainbows.
Why now? I don't know. Why not? But I'd put my money partially on the company's recent win in the Viacom case, and a sense that they've now figured out more effectively how to help the big content owners (labels, movie studios, TV networks) identify infringing uploads, which might tend to fall largely in that longer-form category.
We're hearing something about a "15 minutes of fame" contest to celebrate the expanded video duration, in which winning uploads will be featured on the YouTube homepage in a future spotlight.