It happens but not frequently. I've found that if I sit up front I avoid distractions (side-bar conversations, other people's actions, attractive females. etc)
This approach also makes it easier to raise my hand and participate since I can't see everyone looking at me when I speak.
I go to NA meetings and we don't kick people out. By taking such action would be detrimental to those who want to get clean but simply don't know how. 'The only requirement for membership is a desire to stop using'.
If you sit up front you won't see anyone who may or may not be high. Also, there are candlelight meetings in many areas. The darkness is helpful in many ways.
Give it a try, man. Just try and be honest and have an open mind. Don't allow one meeting to be the deciding factor.
Shit, I just noticed you're in Philly. Shoot me a PM and, if you want, we'll head out together. There is actually an 11:00 PM meeting in the city tomorrow that is a candlelight meeting.