Seriously?  Any first year contracts textbook, or any copy of the UCC.  

Contract requires offer and acceptance.  The offer is when the customer proffers payment (not as some think when the seller advertises).  By accepting payment in return for shipment, then keeping the money (and sending a receipt saying what the seller has sold), the seller accepts that offer.  That is a contract.  All a contract is at its core is an agreement to do one thing in return for another.  The difficulty is not establishing breach of contract, but actual damages.  Just a broken contract by itself doesn't entitle you to damages.  You would have to show you are somehow in a worse position than you would be in had the contract been carried out, i.e., you would have otherwise had an Avalon by now and have made whatever amount of money, and this is somehow BFL's fault.

BFL did not just make the initial contract either.  They continued to make false assurances as to delivery time and even made people agree to further conditions (in return for nothing) just to stay in the queue.  Even if they hadn't originally established a binding contract, and could have probably backed out early on with little to no consequences, just sitting on people's money for in many cases over a year while jerking them around is just not legal.

Even if, somehow, taking money in return for an agreement to deliver a product didn't establish a contract (and if you think that what planet are you on exactly?), consumer fraud and mail order laws have a lot more stringent rules than plain old contract or UCC.  Things like triple damages provisions in some states, like New Jersey.

I can see why people wouldn't want to pursue these avenues, because they just aren't going to be profitable, and if you've been waiting around for over a year for your product and actually still want it, why would you drive the company out of business just when it's actually starting to deliver?  But it's not legal, it's not kosher, and it's a major league dick move in every sense of the word.