YouTube has released a new web uploader that enables you to simultaneously upload up to 10 video clips in one go and each of these clips can be as large as 1 GB in size. Discussion here.

Though you could also upload large video files to YouTube earlier, it required you to download the desktop based uploader software but now you can send big videos to YouTube from the web browser itself without requiring any software.

Other than file size, YouTube had imposed another limit on the duration of the video clip. You were not supposed to upload any video that was longer than 10 minutes in length and I think that was in place to prevent people from upload full movies and TV shows onto YouTube. Not sure if that limit has been relaxed with this new update.