5 years ago, it was 22 hours recorded per minute[1]. That translates to 25 years per week, which is their previous retention term. The volume has probably gone up substantially in the intervening time.
So they're huge numbers, but still pretty small in comparison to YouTube which claims to have 100 hours of video uploaded every minute [1] - meaning they probably have at least several millenia of stored video... wow.
[1] http://mashable.com/2009/05/21/justin-tv-usage-stats/