YouTube makes video length unlimited for some users
The only requirement seems to be for the videos you upload to constitute original content. YouTube says that today's enhancement was made possible by the continued improvement of its tools for copyright owners.
If YouTube ever decides to let everyone upload unlimited length videos (or at least the majority of its users), it will be interesting to see what effect that will have on the quality of the videos on the site, since, like Twitter, YouTube has always been about working within the service's imposed brevity.
To find out if you're in the subset of users who already have the ability to upload longer videos, just click on 'Upload' in the top right corner of YouTube once you're logged in.