Now, I do know that the difficulty auto-calibrates on the "power" of the combined "cloud". My question is different: if more (many more) users come, will the economy of the pool "handlers" change? More users (and greater difficulty) equals more weight on the pool servers (and so less "net" money to pool handlers). And there is probably a maximum number of users a pool handler can handle before his network pipe gets full (and I don't know if the weak link is the network pipe, the processor or the disk). Or will simply increasing the difficulty of the "simple" shares used by pools solve this?
How much powerful must be the pool servers? (or, more importantly, how much less powerful than their clients can they be?)