This is wrong. What is considered public and private is not like you thnk it is. Even if you have a two-person company with 100 shares outstanding, turning around and soliciting purchasers is considered public offering and can only be done after registering with the SEC and complying with their disclosure requirements. Why? Precisely, in part, to avoid the fiasco that the OP is asking about. This is where the libertarian web-of-trust bullshit shows itself to be an infantile daydream. Regulation is a necessary "evil" and throwing out the baby with the bathwater, as Bitcoin zealots are so passionate to do, gets noone any closer to "fixing things".
As far as liability is concerned, those soliciting purchasers and issuing shares via the GLBSE (i.e the companies) are the ones who would be the target of the SEC, not the purchasers.
I'm registered in CA with a registered legal business. However the whole legal shares scenario went over my head. I think for now anybody that is invested in GLBSE will be considered as Investors and not partial owners until I get a proper business license for the allowance of selling ownerships. Good thing I'm still under BOE radar cosindering I only make under $500 in netprofits, shouldn't be long now until I get a proper LLC or S,P,ETC corp..... In fact I'll got to BOE on Monday and tell them what needs to be done!
You're registered so your allowed to have private investors. Legal issues only come in when you offer your company publicly. You need more than a special license to do that. GLBSE is a public exchange as far as I see unless one could legally argue otherwise.