If you are serious consider getting some Asic miners or even Used FPGA miners, rackmounting them is rather trivial and the rest of the servers will thank you for saving them from an early death.
That is what I would like to do with the BTC I raise from an offering on bitfunder. I would like to buy some of the ASICMINER blades as well as placing orders with Butterfly Labs. Then pay out the mined BTC as dividends to shareholders and keep 5%-10% for myself. Once I show that it is making money then my boss will invest some of the company profits into shares to collect BTC dividends.
The problem you run into is that Bitfunder or one of the other exchanges approve it and them???
Mining can be profitable. Mining bonds tend to leave people feeling burned though. Traditional venture capital firms like yCombinator tend to make shitty investments when they move into the BTC space, but They might have some loose money to throw at a mining farm.
Also I haven't checked in a while to see how Avalon is shipping, but I believe the Avalon ASIC units required minimal modification to become rack ready (think the height is 4U).
If you really want to mine something with off the shelf hardware though, at the moment it would be hard to avoid setting up some Radeon 6990s which though hard to find are some hashing beasts. Point them at BTC, LTC, doesn't much matter.
I think bitfunder would approve it. It would be a company and not a bond. As far as I know there are not any companies currently offering a piece of the pie for hosting services as well as mining and the additional hosting services could give us an advantage for buying new hardware over other mining companies. We do currently have a few 7900 series cards but I am more interested in ASIC mining going foward. Any GPU mining would be just to appease shareholders until ASIC miners arrived.