You can't do crowdfunding with bitcoin yet. I noted there's no comments on that so I've started one off.
To do crowd funding you need a pending transaction function. Most cards have it but bitcoin is instant and non reversible so its difficult. You may have a crowd funding vendor that tries it but you have to trust him to escrow the money properly and refund properly on failure to reach quorum.
As Satoshi said bitcoin is about avoiding the need for such trust.
I can see how to fix it by building two escrow systems into some or all wallets for crowd funding and for dominant assurance contracts. The pledge is sent by sending a tiny percent of the promised funds. I.e. 0.1% or so; and storing the rest in a locked file so you can't accidentally spend it. This way your only risking a tiny amount. [The escrow file should also store the two parties, and the completion date of the fund.] these escrow files are never sent anywhere.
When the time is up the system sends you a tiny transaction that flags the three possible states: Project cancelled, Quorum not reached, Quorum reached. Only in the last case does the full amount transferred. If the Assurance contract is a dominant one the contracts creator escrows some bitcoins in the participation benefits file. If the quorum not reached results occur then this bitcoin amount is divided by the number of participants and that quantity of bit coins is sent back.
Crowdfunding and assurance contracts are going to be very important in the future. You can do most public goods and start many private projects using them. You could also crowdfund the bitcoin mining process after 2040! And you could crowdfund Arbitrators to sought out disputes, detectives to find hackers and lawyers to put the case for liberty.
http://en.wikipedia.org/wiki/Assurance_contract and
http://appliedimpossibilies.blogspot.com.au/2012/05/crowd-funding-government.html
