Hey mel ~ Welcome to page two... Have some apple salad.
Your question might get more responses if you post it on the Teachers/Principals forum but I'll still give my opinion here...
Is the open forum limited to PTG topics or are general questions addressed to the principal allowed? I say, questions should be PTG business only. Folks who want access to the principal to discuss any other personal or school related issues should make an appointment with him personally.
I can see the appeal for parents if your principal is difficult to get face time with but, IMHO, it's rude to waste everyone else's time at the meetings for personal issues.
At my last school people took advantage of having the principal and teachers present at the PTO meetings. I had to draw a hard line. If anyone chose to bring up non-PTO topics anyway (despite the clear rule), I'd say, "That's an XYZ issue, please make an appointment to discuss it with Ms. ABC at a later date." And then we just move on. It really is that simple.