Like I said before, tagging is hot. Salon has a nice article looking into the matter, balancing the pros and cons of this phenomenon. I think Microsoft's MacLaurin sums it up best when he says:
"I'd say it's more a matter of figuring out who knows where the good stuff is, and less about finding new friends by tagging. I cannot imagine forming a relationship with someone because we tag our photos a similar way on Flickr."