Judging by this graph showing posts to the dev list (on Gmane) the rate is currently at about 50 posts a day. This has roughly doubled since the beginning of the year. Some of the increase is down to the momentum behind Hbase (which provides Bigtable-like capabilities on top of Hadoop), but I think it is also down to general growth - more people seem to be participating in development than ever before. This is great! Obviously the risk is that at such a rate of development Hadoop becomes unstable, but so far it looks like it's under control - the (informal) feedback I've had tells me the 0.13.0 release is one of the most stable we've done.