You can link to specific log entries. You can get these links for example by clicking the timestamps in the log. Until now, such links to private log entries showed no entry even if you had permission to view private log entries. The links now show the entry.
Admins can use the abuse filter tool to automatically prevent bad edits. Three changes happened last week:
When a filter matches too many actions after it has been changed it is "throttled". The most powerful actions are disabled. This is to avoid many editors getting blocked when an administrator made a mistake. The administrator will now get a notification about this "throttle".
Bots using the API no longer watch pages automatically based on account preferences. Setting the watchlist to watch will still work. This is to reduce the size of the watchlist data in the database.
There was a new version of MediaWiki last week. You can read a detailed log of all 763 changes. Most of them are very small and will not affect you.
Changes later this week
The new version of MediaWiki will be on test wikis and MediaWiki.org from 12 January. It will be on non-Wikipedia wikis and some Wikipedias from 13 January. It will be on all wikis from 14 January (calendar).