I started Carbonite a few weeks ago. Love it.
The initial backup takes quite awhile if you have a lot of files (mine was 46+ gigs and took 3 days). After that, backups are much, much faster.
It backs up all new files as soon as they are saved or installed. All in the background and I never even notice.
Oh, and most of the files are video and audio files. Backs them all up with no problem.