Six Apart recently launched Movable Type v4.01 beta 1 and beta 2 new versions.
Over these two betas the team behind Movable Type addressed the bug reports and patches provided by the community. The issues fixed were mostly related to problems during upgrading and migrating content from previous versions to Movable Type v4.0, but also to developers encountering problems on migrating their plugins to the new framework as well as building up some new and more innovative ones.
On a side note Six Apart announced that beta 2 is the last beta before launching Movable Type v4.01 which is going to happen in a relative short time frame as they started to get us used to.