I have met and made good friend through my interest in photography and web based photography forums. Just recently Matt and I met wit Ian_uk of here down at Silverstone and we have kept in touch since. Previously I met several members from here (staff) and some of the OcuK guys as well from when I used to be active there (cykey/PeteMC, Dave) spring to mind.
So the oppotunities are there and when you all get together its very interesting to see how the "same" pictures turn out differently.
Obviously take care when meeting a stranger for the first time, but by being sensible its an excellent way to meet like minded people that regularly become friends.