When not playing with SPACESHIPS! I managed to get this stuff done:
API Enhancements - Some new functions and tweaks to existing ones. Details are documented at the API page.
MOC Designer - Several changes to the MOC submission page. If you are building an alternate/mod/subset there is a new option to pre-populate your parts list with the parts from the set you choose.
Inventories - Admins and MOC designers can now make bulk changes to sets or MOCs. For anyone making these changes, please be aware that they are immediately visible to all users.
Set Layout - I tweaked the layout of the set/moc details pages to try and reduce the clutter and make the important stuff easier to find. I also made use of the Brickipedia API to display short description snippets from the wiki pages describing the set.
Bricksafe Integration - I have started to make more use of Bricksafe on Rebrickable pages. If a MOC links to a Bricksafe page with images, those images will appear on the MOC's details page. Later on I will provide more options for the designer when submitting their MOC, for now it's automatic.
Other Fixes - Fixed issues with: Lost Parts editing; use of mixed case emails; non-ascii CAD file uploads; improved MPD parsing; pick set sliders; changing MOC/Set images no longer allow invalid URLs; Build searches now include sets with > 1050 parts.
Other Stuff - I setup Twitter cards so if anyone bothers to tweet links it will show full photos and descriptions. The "Buy this part" table on parts details pages is now initially collapsed. Added a new admin tool to help with creating new parts.
If you have suggestions for a change or new feature, you can let me know via the Suggestions Forum.