I just met my first in person geocacher today. He walked up on me while I was hunting his cache. It was a pretty funny scenario, but basically, he seemed like a really cool kid. 'Kid' to me being 13. :-) I could have stood out there and talked to he and his dad for days, but alas, I had to leave.
That being said - the geocaching community is probably like many others. It's probably mostly really cool, fun people, but there's going to be some people you just don't get along with. Same goes for any large group, be it an office, a sporting team, PTA, whatever.
As for the forums, the internet has a strange way of making some people much 'bolder' than they would be in real life, as somebody else had mentioned earlier in the thread. Some people are 'bold' in real life. So again, in my opinion, it's like with any group, hang with the people you like and just avoid the ones you don't.
And most important...have fun.