What the heck, let's pull in another state in another circuit, Iowa this time: Brunsman v. DeKalb Swine ( http://caselaw.lp.findlaw.com/data2/circs/8th/971135p.html ). This opinion points to the sections of Iowa Code relevant to warranty disclaimers, and states: "Under Iowa law, a court considering a claim of unconscionability should consider the factors of assent, unfair surprise, notice, disparity of bargaining power, and substantive unfairness." This plaintiff lost because the warranty disclaimer met the applicable statutory standard of wording and conspicuousness ( http://www.legis.state.ia.us/IACODE/1999/554/2316.html , if you're curious) -- the existence of such a standard implies that the state's law does not view such a disclaimer as substantively unfair -- and it was a properly negotiated agreement in the other four respects named.
It would not surprise me to find that many jurisdictions have a similar technical standard for disclaimers of implied warranties and that the language of the GPL meets them. But clearly there's more to it than good drafting and nominal assent, even if that assent were demanded before use and not just before exercise of copyright license. In the event that Linux, glibc, and GCC destroy the market for commercial UNIXen and their compilers (as they bid fair to do), and crowd the BSDs at least out of the server sector, that "disparity of bargaining power" factor may yet undermine the GPL's warranty disclaimer and expose distros (if not upstreams) to liabilities they hadn't planned for. Cheers, - Michael (IANAL, TINLA)