New follower processing using the Social Graph methods will become a bigger and bigger headache as more and more Twitter accounts grow into the "must page" territory.
I thought I'd put a completely different approach on the table and see what everyone thinks about it. When doing new follower processing, one is not really interested in the full follower list. You just want to know when a new follower action happens on a Twitter account. To me, this sounds like a perfect candidate for a pub-sub architecture. Instead of Twitter taking on that additional infrastructure load, I'd recommend you investigate whether you can make new follower actions available via Gnip.com. Gnip already has the ability to segment by people, tags and keywords, so segmenting the transactions by Twitter screen name should fit into their current architecture. It's a win for Twitter, because you push a new follower transaction out once only to one single service, and you're done with it. Us developers then grab those transactions from Gnip. It's a win for us as well, because grabbing those transactions don't impact our site rate limits. This pub-sub approach could work for a number of other developer needs as well.
