Hey, I used an email list (uploaded to gmail) I had to invite people as friends to a FB account yesterday. +/- 500 emails, 400 had a FB account on it, the rest received the invitational email. After a minute, 10 of them accepted and boom. It stopped. Not one of the remaining 400 has accepted the request since then.
It shouldn't be even considered blackhat, since I know who these people are (although I don't know 99% of them personally
) and I'm adding them to invite them to a group that should be of interest to them - and has nothing to do with selling anything, or making money any other way, ever 
possible problems that I've thought of:
1) it's mostly girls 15-16yrs (some kind of FB protection? Don't know..)
2) they don't have mutual friends with the profile
3) the profile is new (although I tried something similar in a lesser scale with an aged account later and the success rate was even lower)
Three of the 10 sent a message asking who I am and when I explained why I added them, they all accepted. But still. Did facebook somehow null my requests after a few people denied them, or?....
It shouldn't be even considered blackhat, since I know who these people are (although I don't know 99% of them personally
possible problems that I've thought of:
1) it's mostly girls 15-16yrs (some kind of FB protection? Don't know..)
2) they don't have mutual friends with the profile
3) the profile is new (although I tried something similar in a lesser scale with an aged account later and the success rate was even lower)
Three of the 10 sent a message asking who I am and when I explained why I added them, they all accepted. But still. Did facebook somehow null my requests after a few people denied them, or?....