I go out of my way to deposit the greatest amount of bullshit possible into marketing campaigns and folks who collect personal info for no good reason. I think the mailman wonders if I'm some sort of multiple personality guy after the day he asked me who four people were he was delivering mail for at my address and I told him they were all me, sort of, but not really (none was actually for me).
So the first time I got a Plaxo message (it was poorly formatted for a non-html mail program) I deleted it thinking it was a virus that infected someone's mailbox.
Then the next one came. After some serious thought, here's what my response is to folks who use plaxo:
I have no interest in adding that much info about myself to some random company's databases for no good reason. If you want to contact me, you know how already, obviously, so use that piece of info and don't be so lazy, and update it by asking me personally. Otherwise, why are you asking?