I do wonder what legal recourse you have (if any?) if you are lied to when you make the investment? If someone tells you they are a company, (company = incorporated) and you invest, do you still have this liability?
I've bought a lot of stocks on etrade and I don't think I've ever dug up their actual incorporation paperwork.
Generally speaking, you're expected to conduct due diligence. Generally speaking, those making an offering should provide sufficient information for you to do so relatively easily - company numbers, licence numbers, etc. You can very often verify basic information about a company free of charge, so it's becoming more and more difficult to justify not doing due diligence.
A blatantly false claim - saying that Microsoft has invested in a company, for instance, when they haven't - designed to mislead investors into a false sense of security can shift liability, though, especially if it can't be easily verified. At that level, though, you're often looking at investors wanting to examine the company's books before making an investment so it's a different ball game (and at that level, the amount of due diligence expected is considerable).
It's probably also worth pointing out that the extent to which you're involved in company activities often determines liability. "Investor" is a generic term and the means and manner of investment often have a great deal of bearing on liability.