We’ve just seen a very large drop in the volume of tweets coming across all streaming API endpoints. For instance the sample API has gone from around 90 tweets per second to 20 tweets per second. The same sort of thing can be seen on keyword and user follow streams.
Our logs show this appears to have started at about 2015-01-06 00:50 UTC (35minutes prior to this post). I have tested this from 3 different locations as well with the same results (US, DE and AU), and with different credentials.