Version 2.5 of my HashTag plugin has now been released. See the Hash Tag Plugin project page for more information.
The major change in 2.5 is the ability to tweet scheduled posts, currently that uses the default settings for the plugin at the time the scheduled post is published.
So what will be happening for Version 3.0? Well there are three things planned:
Support for MT5.x and Open Melody.
Using OAuth to link to your twitter account.
Store tweet options with post / page so that default options are not used for scheduled posts and you can set if the plugin should retweet when you edit a page.