I give up. What is pool hopping?
I believe 'pool hopping' refers to switching pools at certain times to take advantage of the proportional payout system.
With the proportional payout system, the pool mining effort is divided into rounds, each round ending when the pool finds a block. The pool asks users to submit shares (solutions for an artifical, low difficulty). At the end of the round the 50 BTC reward is divided between the users, weighted by the shares they have submitted. (transaction fees are almost always kept by the pool and there may also be a fee).
One issue with this is that as a round goes on, the shares become less and less valuable. A miner can make quite a lot more (I'd guess a bit more than 120% of solo mining in real-world conditions) by connecting to a small number of large proportional-payout pools and always channeling his shares to the pool with the youngest round. Proportional pools try to combat this by not immediately publishing when a new round has begun but this is not 100% effective.
To be clear, the pools do not lose money because of this (or other tricks such as griefing), the other pool users do. Also, some people view this tactic as a form of cheating so you may find pool operators trying to block or ban you for such behaviour.
Switching pools when one goes down so that your miner is always busy is typically not seen as a form of cheating.
