CBT, agree it was unprofessional, especially while tweeting in real-time.
When I had a MySpace page I refrained from making negative or derogatory comments about the production I was working at the time, only general positive statements ("Great rehearsal today" "I love my crew" that kind of thing); even afterwards when the production was over I would keep comments to generalities. No, "Oh my God, I have no clue why they cast so-and-so as Vivian, she was terrible!"
Once I did mention from a rather difficult production that I learned more about conflict resolution than from any other job I had. That was about as specific as it ever got, and even that may have been too much. With MS or FB or Twitter, you just have to think twice.