I listen to the network (via http://bitcointalk.org/index.php?topic=2808.0
), and while transactions generally come pretty randomly, there is occasionally a cluster of a dozen or so transactions, coming very quickly, within a second or two. It took me a while to realize that when these happen, it is always the top of the hour. I don't notice them every hour, but several times a day, always on the hour.
Looking at blockexplorer, it looks like these are a series of small payments, a few cents or a few bitcoins, generally from high value transactions near 50 btc. And they each normally have a 0.01 btc transaction fee.
An interesting pattern...