YouTube has begun lifting the previously-enforced 15-minute video length limit for some users. The limit had been raised to 15 minutes for all users (up from 10 minutes prior to that) back in July. As of today, users "with a history of complying with the YouTube Community Guidelines" and the copyright rules that YouTube enforces will be able to upload videos of unlimited length.
What are the Requirements?
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.