I noticed this at the weekend, the problem continues. I can set up a tweet to send when a scheduled post publishes, but the tweet is not sent. This worked on 21st June, failed 22nd June. The only update I think I've made in the timeframe is the update to Jetpack 2.3. Is anyone else having a similar problem?
I've now updated to WP 3.5.2 - see if that fixes the problem. If it does/doesn't I'll report here again in 24 hours.
Running a Photocrati theme and 12 plugins