I'm back with 800MH, in a few weeks 2GH.
Over an infinite time period, PPLNS is not unfair to part-time miners UNLESS they are deliberately hopping at or before the expected halfway point consistently.
Sure, sometimes you will do 4 hours mining at the start of a long block and be credited for nothing, but sometimes you will do 4 hours mining at the end of a block and be credited as if you had been mining the whole block.
No that's not correct. If you join at the end, you'll get your percent of 750000 shares depending on pool hash rate. If it takes the pool 4 hours to hash 750000 shares, and you join at the last 4 hours, then you will be credited as if you were mining the whole block. If the pool takes 8 hours to generate 750000 shares, then you get half of what you'd normally get for a while block - but this is same as proportional so that is okay. But if you left early, you'd lose there too.
I don't think this is really going to stop pool hoppers...instead of hopping in at the beginning, now just hop in NOT at the beginning - such as at 75% of difficulty and staying to 125%.