The Steam Client Beta has been updated with the following changes:
Steam Achievement SetsA new way to organize, track, and complete a game's achievements. Read more details in the announcement.
Games can now organize and group achievements for base game and DLC content
DLC achievements can be added via sets without breaking game completion
Completed achievement sets remain completed when new sets are added
Achievements and sets can be archived if they are seasonal or can no longer be...
The advantage to Steam going 64-bit is that most people can now remove all their 32-bit libraries.
Previously you needed 32-bit libraries for most of the actual games you ran through Steam, so it didn’t really matter if Steam used them too.