CPU-only mining that is botnet resistant and also limits the sizes of pools is very much needed.
So when can we expect that to appear?
Q1 2014
How could CPU mining be botnet resistent? What's different between a computer in botnet and a normal computer?
Memory. The average botnet node is a 5-10 year old machine (most commonly Windows XP). A memory requirement larger than the average memory of botnet node that also increases at the rate of Moore's law (or possibly below it as a margin of safety) would be highly resistant to botnets.