...is that I'd like to known exactly what Facebook advises its users about invitations.
I find the closing words of the subsequent emails particularly disconcerting: "This e-mail may contain promotional materials. If you do not wish to receive future commercial mailings from Facebook, please opt out(link)". So firstly, thanks to someone I know, an address I gave out in good faith it would remain spam free is on someone's mailing list without my consent. Great.
Secondly, if the opt-out link were to mean I'd never be notified again (as would be decent) then they would have to transfer this address to another list just as easily wrest from them by hackers - which appears to be the case from the version of the linked page I last saw (presumably it's also shown to their own users who opt out of emails, and retaining my address permits some kind of "who invited whom" procedure. But I digress). If not, my friends' persistence gets that address (or its replacement) back on the list regardless of how frequently I register my displeasure.
On one hand I feel like a cantankerous old f*rt flagging them "is spam" without following the link, but on the other it feels *very* right to.