There are still five proportional pools, and all being merrily hopped with hashrates between 500 and 1500 Ghps. However, afaik GPUMAX can't be used for pool hopping.
From what I've heard, not only could it be used that way, it actually was on a fairly spectacular scale. Whilst you couldn't schedule when you'd receive the shares you'd paid for you could apparently change which pool they went to right up until the moment your order left the queue. I believe proportional pools saw huge spikes in hashrate from GPUMAX at the start of the round, and once there weren't any big proportional pools anymore the demand for hashpower on GPUMAX dried up and remained that way.
The simplest explanation given the evidence:
GPUMAX was established to serve as a mysterious black box for lending superficial credibility to BST.
I'm not convinced it started out that way, but that is the most obvious explanation for it right now. For instance, why would pirateat40 say that he's going to direct more effort into it when the market for it has gone away and is unlikely to ever return?
Oh, and on a more on-topic note, the death of pool-hopping is an interesting example of how actual high-return opportunties tend to be short lived and have very limited capacity. In order for pool hoppers to make money, naive miners had to irrationally continue to mine at proportional pools 24/7 despite that losing them considerable amounts of money compared to either pool-hopping themselves, selling their mining power to hoppers on GPUMAX, or even just using a non-hoppable pool. As more miners realised this, pool hopping was inevitably going to become unprofitable. (It also didn't help that large-scale pool hopping was very disruptive to the pools, which needed vastly more server power in order to handle the surges from pool-hoppers but didn't get a commensurate increase in income.)
