Interesting to see large amounts of transactions happen exactly on the hour (or sometimes half-hour). What's up with that?
Some people have scripts that automatically move currency to either: 1. themselves at a different address in a misguided attempt to make their coins more anonymous. 2. to (nearly) continuously pay for something, in a certain case people are actually renting bitcoin mining servers, with bitcoins. Yeah, it's kinda messed up, but it comes down to the unknown forward difficulty rate. The person renting out the server thinks that it will go up in difficulty more than the person that is renting it.
My guess would be that these are payouts from a mining pool. People pool their hashing capacity to collectively find a new block worth 50 BTC and the pool then splits the reward between the participants. Some pools probably do this payout step on a fixed schedule.
On the other hand, most pools have moved to include several recipients into a single transaction, so if it is a pool, it's somewhat "outdated".