It's probably related to a new hack that intercepts/fakes the in-app purchase calls on jailbroken phones; it allows the user to get "free" in-app purchases, but with invalid receipts.

I'm sure a lot of devs weren't checking receipts and got stung by the hack. So they started verifying receipts, traffic goes through the roof, Apple's servers fail under the load.

Been watching what may be the server side of this hack for the last week or so...it's not very subtle and retries obnoxiously enough to stand out/get itself blacklisted.

It may also be possible that some developers' apps aren't catching duplicates or thresholding these calls and are checking receipts with each hit--that'd put a lot more load on Apple's servers, too (though I'd think the app developers would notice this change in traffic as well on their side?)?