From PayPal Support @ 8:56AM PST today - Our technicians identified an issue late yesterday which was causing IPNs to be delayed and subsequently resolved the issue. Since the IPNs were queued, they are being sent in the order they were queued. Our technicians have stated that we should be getting out from under the queue shortly.
From PayPal Support @ 12:34PM PST today - Unfortunately, it looks like the delay issue is still occurring. I've added this case to the issue and we're tracking it as we speak. I'll update you right away when I know that the backlog will begin to clear up. [i.e. The problem still is ongoing and not resolved per the previous update]
We have had no updates, but I figured I would at least give folks some information. Sounds like a decent size problem that hasn't been resolved. We have had no movement on our queue since yesterday at ~2pm PST.