I personally don't see the point behind having shifts at all.  We find a coin, we get paid.  I don't see any sort of delay.  The amount I get paid is based on the amount of hash I do over the length of the coin.  If someone jumped on and put 500,000 hash into the pool for a day, all it would mean to me is I'd get paid a little less because of the hash jump and as soon as person left, I'd be back to normal.  Inbound jumpers to me only means we'll get that BTC a little faster then when they were elsewhere.