Flew from Seattle to Baltimore and vaped all the way. I was discreet and had no problems. I think it helped that the people in the seats next to me were my friends
No problems on the way back either. However when reading the American Airlines magazine on the flight I did not ice it said that e-cigarettes must be turned off during flights. Since they didn't mention it in their pre-flight talk (along with the no smoking stuff) I ignored it and stealthily vaped away.
No problems with the TSA screeners either. I think they all know what e-cigs look like now