Why the HELL would people use this?
Case A: You get more coins than what you pay for.
Miners are getting screwed.
Case B: You get less coins than what you pay for.
Buyers are getting screwed.
On the mining side, it's easy since the payout is ~105%.
For the lessors the idea is to be able to "burst" your hashing capacity if you feel you can gain an advantage in doing so.
Find a pool overdue for a block, throw a bunch of hashing power at it, collect bonus for finding block (or get a bunch of shares loaded in at the end of the weighting period I suppose.)
There are a few unscrupulous things someone could do with enough hashing power, a couple nefarious ones, and several reasonable uses.
There is also the interesting question as to what happens if the difficulty goes down...
Of if someone buys up 5-10% of all hashing power and routes it to a null pool to get the difficulty to GO down (like paying farmers to NOT grow corn.) (not sure of the motivation WHY you would waste BTC this way)
Heh, if I'm right we might get some government or other large entity paying folks NOT to mine BTC at some point in the future. Who says you can't regulate bitcoin? Maybe we can all get bailouts by the time we split to 12.5!