Do multi-signature transactions make a 'bitcoin kickstarter' possible? And what state are the bitcoins in, in the meantime?
While multi-signature transactions with a trusted party (e.g Kickstarter Inc.) would work, their disadvantage is requiring said trusted party...

The bitcoin wiki describes a different method that doesn't require any third party:


Each backer creates a transaction with the amount to be pledged (this is an immediate step and required since the method doesn't allow for change
That transaction is used as input signed with SIGHASH_ALL | SIGHASH_ANYONECANPAY, and the output is the to-be-funded address with the funding goal. Due to the input being less than the output, this transaction is invalid and shall not be published but instead transmitted to the recipient.
Once the recipient received enough transactions summing up to the funding goal, they can publish the assembled transaction


Unfortunately, this method has other drawbacks:


The funding goal must be exactly met (or a multiple of it), i.e. there cannot be stretch goals or overfunding
Since the input transactions are not spent until the funding is complete, the backers might accidentally spend that very transaction in another transaction




Ideally, script would provide means to determine whether a given bitcoin address (or in this case, the script itself) currently has at least a given amount of bitcoins available...