I also sell mining contracts on ebay which is going quite well. I'm not one for ripping people off but people seem to buy my contracts for a couple of pounds for just a few hours on my 5GH/s rig.
I too have thought about selling time on my ASIC's. My concerns are that someone will buy a short term contract. Then after you have mined for them for a week or two, they try to reverse the transaction and now they have stolen your electricity. How do you prevent yourself from getting burned?
Woodser