If a site uses a US based hosting company, domain name (e.g. .com), or payment processor, those services may still be cut off, even if the servers are out of the country.

I doubt they would have any legal basis for extraditing a non-US-citizen for a SOPA violation, but there have been attempts to pursue charges against foreign citizens for notable DMCA violations if they enter the US, so that could continue to be the case with SOPA. If a US citizen uses a foreign server, I doubt that would shield them from legal action.