On the one hand, I prefer to judge people on who *they* are, rather than who their friends are; also, I have certainly been in the situation where I have two friends who don't get along and it doesn't affect my ability to enjoy them both separately from each other.
On the other hand, unless the name-dropper is someone I know very well, like very much and have a lot of interaction with (this applies to maybe 5 people in the universe), I find it very difficult to trust or talk to someone who is friendly/ close/ et cetera with someone who has done unspeakable shite to me. I also think who a person's friends are says something about who they themselves are, and while I realize everybody has mixed good/bad likeable/unlikeable points, if I have a choice I will pass up the chance of being friendly with someone who might turn out to be an Asshole Just Like Their Pal So-and-so, in favor of someone who doesn't have any dead weight.
I have been turning this over and over in my mind for literally years. In at least two cases I tried to make amends with the Asshole point of the triangle just for the sake of laying it to rest so I could get on with my life, maybe be friendly with both people. Amends don't seem to take very well with me, though. All I got for my trouble in trying to be friendly again with past jerks was my hand bit again, in much the same way it had been bit the first time. So I don't try anymore.
I've reached the point where I basically communicate with about five people close to me, unless I have something specific (music, law practice) to discuss with someone outside that circle. There are lots of people I find nifty in some respect but also find them very untrustworthy in some respect. I am not sure how to resolve this. I'm not even sure if it needs resolved. Maybe I'm only meant to trust a handful of people, and yeah, I'm happy with that. I'm just not sure what to do with the Great Middling Middles.