To cut down on the amount of spam/porn accounts, I've set our network to moderated membership. A couple of times a day I go through the backlog and approve/decline members.
Something that would be an immense help when going through this process is to know whether someone invited the person to the network and, if so, who. Especially when dealing with cases where the person filled out so little information that its hard to tell if the account is legit or not, knowing whether or not someone invited them would go a long way to determining if the account should come down on the side of approval or decline.
Since this information is available in the invited membership list, anyway, it doesn't seem like it would be that hard to add to the approve/decline screen as well? (I say, hopefully.)