Renee Blodgett has a great post on how she uses LinkedIn. She also talks about the awkwardness of turning down people who ask for introductions and suggests that people should not take ‘rejections’ personally.
It is interesting to see how virtual worlds sometimes call for new behaviors. There are indeed a variety of reasons why you might reject someones request – bad timing, not knowing the person well enough, feeling like you are abusing the social capital you have with the person that someone wants to get introduced to, etc. And turning down someone for many of those reasons is not a personal reflection of what you think about that person – although sometimes that may happen also.
I would also join her in asking people not to abuse the system – it is indeed a valuable tool!