@NVZ Each device using the Stack Exchange API gets a quota of requests it can perform each day. Unauthenticated clients get 300, and everyone else except Smokey gets 10,000. Smokey gets 20,000.
@NVZ that wouldn't help. Our biggest spammer group (and I assume the majority of the others do this too) has their human workers register an account and then either manually type out or copy-paste some text into a question and then submit it. They get paid when they show some sort of proof that they posted it (we assume a screenshot). Anyway, forcing registration wouldn't do anything because it's humans, not bots, doing the spamming already.
How do we know this? One of our members (I think Undo) went undercover a while ago and tried to sign up to be a spammer.