Diego explains why the spaces beta isn’t out and also outlines the work that he is doing on the storage system. It looks like he is going to sacrafice a little bit of disk space in order to use less than 64 megs of RAM:
The new version will take up maybe 10-20% more on disk (with a higher peak usage as well), but will have upper bounds on the RAM used. The goal is, again, never to breach the default maximum JVM heap of 64 megabytes when the number of items stored (email, RSS, calendar entries, etc) is 100,000 (yes, one hundred thousand items).