I can't see the point of Plaxo except to gather information about people whilst purporting to do you a favour of updating you address book - or have I got it wrong? The phrase "We have no plans to - - " is vague and does not inspire confidence in me and suggests that they will do exactly that in the future. Even if it read "We guarantee we will not - - ", I would still be very suspicious.
I never give information like that to anyone, not least some totally unknown organisation, to do with whatever they might want.
If your friend wants information from you then why doesn't he/she ask you personally instead of going through some seemingly dodgy third party?
I'd treat them similarly to their (almost) namesake and tell them to get stuffed.