Not sure exactly how to comment on what James Phillips (NorthScale) says about Membase Beta 2:
We released membase beta 1 with some features not yet complete. We felt it was much more important to get the core technology in the hands of users rather than hold it back until all the bells and whistles were installed. Beta 1 delivered a high-performance, elastic, persistent, reliable, replicating key-value store which is on-the-wire compatible with memcached (so it already works with tens of thousands of applications and virtually every). Beta 2 begins to deliver the bells and whistles. The major piece of added functionality is the ability to store datasets that don’t completely fit in memory.