I've been told that it's acceptable to ask about their burn rate (assuming they get no more $ how long will they stay in buisness if they don't turn a profit), is this an acceptable question? Are there any other questions you would ask?
If they consider it to be unreasonable to tell you how long they're going to be able to keep you employed go elsewhere. I've can't remember ever having a problem asking this question (e.g. not joining a startup that I in retrospect wished I had) or ever being lied to, although we can be sure others have had the latter problem.
Other important things:
Try to make sure they can fire people. The only thing worse than a bad hire at a startup is when the leaders don't have what it takes to remedy it. It's hard, it requires the ability to be at least a little bit cruel, but it often is utterly fatal if they can't do it.
Assuming you're a programmer, make sure they give you a test to see if your peers who have also been or will be hired though this process can code their way out of a paper bag. See above, plus you just don't want to be working in a shop with too wide a variation in programming ability or at least too many lows. I suspect I don't have to tell you the latter given your current background but I note it's much less affordable in a startup. So are lies. The one time I knew ahead of time that my boss was a liar and I went to work for them anyway (was very desperate due to a cold cubicle that was making me sick) I really regretted it.
Do the Joel Test: http://www.joelonsoftware.com/articles/fog0000000043.html
Nowadays, I'd make sure they have a grasp of Customer Development (search this site for that) and otherwise look like they have a clue WRT to business. That tells you unambiguously why stealth startups are generally to be avoided. Looking back on most of my career I sure wish I'd known of its concepts and it certainly explains the failures of many of the failed startups I've worked for.
http://www.innovationontherun.com/considering-working-for-a-...