The concerns about the project turning to vaporware are legitimate concerns and were ones that I myself raised in my mind prior to donating.
What made me decide to invest some money into the game were the following lines of reasoning:
1) Chris Roberts has a solid track record in delivering products - and in particular, quality products - throughout his professional carreer. He has a good reputation that I do not think he is willing to squander by doing a "take the money and run". I also think, based on his track record that he will produce a product. Wether or not it lives up to its promises remains to be seen (but that is always the case with any product, and is a particular concern with MMOs who never deliver on all of their promises). I believe he will deliver a product that is not a slapped together contractual obligation product "because he had to give the investors 'something'" and is of some degree of playability that would have been worth my "prepurchase" investment. The man is driven by a passion to create a product that he has been dreaming of most of his life and this is his chance. I think he is going to do his best to deliver on that dream and I think he is the kind of man to honor his commitments.
2) The entire team is made up of seasoned, well respected, and reputable developers/employees from related industries (and yes, I checked out of sheer curiosity - I even realized I casually know some of these people over the years through mutual friends in the industries). I believe that this team will deliver a product of higher quality than a contractual obligation thrown bone. As a fun aside, the person who is designing the spaceships is a well regarded hollywood studios designer who is most recently well known for designing the ships for the Star Trek reboot movies.
3) As has been previously noted, Kickstarter has very clear contractual obligations on delivery. Even without that, there is a contract to deliver in their independent funding source. Were they not to deliver any product whatsoever, there are multiple avenues, contracts, and breaches of promises to utilize to get your money back. Kickstarter in particular will have an easier and established way to initiate legal reprisals for a return on investment. In a nutshell, the avenues for a refund are established and clear cut, making for a reduced risk should Roberts attempt a "take the money and run" move.
4) The promise of the single player game was a great incentive for me. I decided that even if the MMO winds up not to my liking, I was happy enough to invest the equivalent of a retail price very far in advance pre-purchase for funding the developers of similar games that I enjoyed so many years ago in the chance that at least the single player game would be fun. If I wind up not being pleased - well, I have wasted more money than that on things I wound up not liking and I was willing to take a chance on this. I think this has a greater chance of a positive outcome than some other things I took a chance on in the past that worked out well.
5) It seems to me a nominal value for a combination of what seems like a decent chance at a fun game plus my willingness to express my appreciation by helping to keep the team employed/funding their future endeavor for what was far more pleasure for dollar value out of these people's previous works than I ever paid for their work in the past. I made out like a bandit with the tiny amount of money I paid for their products in the past compared to the effort they put into said products. If I thought points 1 - 4 were not valid, this would not be a consideration, but it was the one that pushed it over the edge from hestitation to giving them some cash.
They have plenty of funds to build this thing by now, so if you are concerned, just wait and see. No pressure. Watch and see what happens and when they get close to release, evaluate and consider. Or wait for release - no big deal. But, for those who do donate and thus are "locked in" to giving this thing a go at launch, please post so we can organize ourselves a bit. If you are intrigued and think that if close to launch, if there is a viable product for you, that you would buy a copy, awesome, post here, too - I'll count ya as a probable for the purposes of a Saighdear when we get closer to launch. I am a pretty risk adverse kind of guy, but the investment of a prepurchase price with all of the points factored above make me think that it is a nominal risk to take. If you think otherwise, that is cool, just wait a while and re-evaluate - I won't think any less of you for it.