PPLNS is simple. At the moment N=902850 (half of the current difficulty), so when we find a block, the latest 902850 submitted shares get paid (50 BTC / 902850) = 0.00005538015932406342 BTC per share. If the round is shorter than 902850 shares, then latest shares from the previous round(s) get paid again until we reach 902850 shares into the past. If the round is longer, then the oldest shares from the start of the round will not get paid.

This means that:

• if you mine constantly, your earnings will average the same as on PPS (but in the short term, luck is a factor)
• pool-hoppers don't earn anything extra
• if you stop mining for a while, your payout from future blocks starts shrinking (because the "payment window" keeps moving forward, and less and less of your shares are in it), but you may still get paid from multiple future blocks if the rounds are short
• when you start mining, your rewards from future blocks ramp up similarly as they ramp down when you stop
• there is no unfair penalty for intermittent mining on average, but the pool's luck does affect how much you get

The difference PPLNH makes is that instead of the last "N" shares, every share from the last "N" hours gets paid (not a fixed sum, but so that we spread the 50 BTC evenly to all shares submitted in the last 48 hours for example). Otherwise it's the same: old shares can get paid multiple times if short rounds follow, or not get paid if long rounds follow.

The exact choice of "N" shares or hours doesn't matter on average, but the larger it is, the less pool luck affects the payouts, but it also takes longer for the payouts to start or stop coming.