As was stated before, the P.E. who sealed the drawing, document, report, etc. is "resiponsible." However, the plaintiff party will sue everyone - P.E., E.I., drafters, the company as a whole, the liability insurance, the client of the property, managers, janitors, the damn goldfish in the aquarium - EVERYONE.
What they really go after is the money, and the suits start dropping until the plaintiff finds who has the (deepest) money-bags and hones in on that target.
I've known Engineers that "freelance" and have no pro. liability ins. As for me, I could NEVER operate that way - all that stuff scares that dog snot out of me....
Their rationale, if something goes wrong, don't be a target, if you have something to sue over, then you will get sued (of course they have "other" asset protection). Afterall, a lawsuit is like any other monetary endeavor - you want to minimize effort and maxmize return. If they know they can't get anything from you, they probably will spare the expense and focus effort elsewhere.
Of course there are other things besides a lawsuit that could hurt you, like losing your reputation and/or your license (P.E. OR E.I.). Depending on the state's rules/laws, even if you don't stamp your drawing, you could still be liable as the P.E. of Record, AND (in at least two one states where I was registered) it is actually a misdemeanor to produce and issue an unstamped drawing!! In one of these states, the board operates an Inspector General's Office that investigates stamping issues, and has legal authority to press charges on anyone breaking the board's laws. They accept anonymous tips too, which means if your drawings/docs are not properly stamped/sealed and your competion gets them, they can turn you in! Yes, the engineering business can get that cut-throat - It's a Geek eat Geek world out there.....
My approach, if I work for a company I make sure I understand the liability coverage. Some companies don't cover you if you're "contract." I don't "freelance" or "rubber-stamp", and I'm asked to do so all the time. I simply say NO and walk away.... I always do my best and strive to learn and continuously improve my skills, this in conjuction with a strong code of ethics is the best "suit prevention" insurance for the money. Use this approach in addition to good liability coverage and you should be fine.