I personally think it's a good thing. Laughter is contagious and I'd rather be around a happy person. But I understand where you're coming from, I laugh for really long periods of time, too. It's embarrassing when everyone else has gotten over whatever was funny and I'm still sitting there trying to hold in my laughter.
I think the worst time was when my bf was trying to be sweet and romantic and I kept laughing in his face, poor guy. He was all "Thanks Harleyq, you really know how to set the mood..."