In my opinion, for whatever that's worth, many don't mine here because they end up with the "bag of pennies" issue with allot of small payouts which causes high transaction fees. Once Kano gets finished with his long awaited accounting code then multiple block payouts can be consolidated and miners won't be stuck with such large fees when they go to spend their earnings. So I think that will make a large difference and cause some hash rate to return. Going PPS is NOT the solution nor is shortening the ramp like slush does.
I wish Kano would have waited to offer the 10 BTC bonus until after the new accounting code was implemented. That would have had a much larger impact, I think.
That's not necessarily true as the payments on slush can be more numerous if one kept cashing out at .01 every time. It would be nice to keep the threshold higher at kano's but I don't see that as a big reason why bigger miners aren't here. October and February are better examples of why they left.