A lot has to do with one’s own associations with a name, too. I worked with a Garrett...so I’d have a hard time writing a character without him slowly morphing into that guy, for better or for worse. Even if I liked the person a lot, I’d feel a little funny about, say, writing little lovey-dovey lines for ‘em.
It’s why I’ve never used the name Tim or Timothy, though I do like the name. Among others.
Though...come to think of it, I guess I know people by most of the names I’m using in my story. So maybe that’s only true for a few names.
I’d still want to use certain names only for people very unlike the real life people.
I have the opposite problem in real life. One of my coworkers is a dead ringer (voice, attitude, mannerisms, motives, everything) for Jayne Cobb in Firefly. Except Dave doesn't know enough about weapons or infantry tactics.
It's the story of my life. I discover a good SF series after it goes off the air. I missed eight years of Stargate SG1's run that way.
I've avoided that problem with SG Atlantis. Thanks to internet newsgroups, I've already watched the first four episodes of season four. Of course the first two were screeners, which is an interesting experience. I think I'm three or four months ahead of the Sci-Fi channel on this. Thank you, British commercial television.