1) update.bml now has a wysiwyg mode (which is still buggy right now, and which currently makes you lose your text if you switch in the middle).
2) you can now post to communities by clicking the pencil on their userinfo, and supposedly the non-members posting feature is now active (?).
3) new style, "Digital Multiplex", for all users in S2.
4) Future stuff (for this, probably just places where they need to be mentioned):
INVITE CODES! They may be changing/going away. New account-creation anti-abuse measures.
Another new style coming up.
Probable changes to permissions and permissions interfaces.
Feel free to mention other new things, or changes to old things/bugfixes that need to be documented, or make new posts about them (always good, especially if you know where it needs to go and/or have proposed text).