Lol, u made me google that.

Yeah, micropayments might work in some cases, in others, maybe deposits; ie instead of paying 8$ for Twitter per month, a one-time 20$ deposit you can get back at any time, but you could lose for spamming. It would be cheaper than $8/mo for users in the long run, but more expensive than $8/mo for abusers (since $20 is more than $8).

Or, a "pass" which for a $20 deposit that you can use ANY site. If they wanted, they could do a cryptographic proof that proved you had the pass w/o revealing who you are.

Also, imagine something hashcash-esque. Like 1 tweet would take 50% of your phone's computational power for 1 min. If nothing else, no one could build a bot to do more than 2 spam tweets a minute, considerably reducing unwanted replies.