There are several ways to be notified of new releases:
Via this forum or Reddit
Major releases and pre-releases are announced on the PhotoStructure subreddit and in the Announcements category in this forum. You can subscribe to posts in this forum by clicking the bell in the upper right corner, and then pick “Watching” or “Watching first post”:
Via Github
If you have a github account, click “Watch” > “Custom” > “Releases” on https://github.com/photostructure/photostructure-for-servers
Via Email and Twitter
Major releases are announced via the email list (subscribe here) and via Twitter @photostructure.
Release notes
Release notes are updated as features are built (rather than when they are shipped, so you can see what’s coming):