A Google Webmaster Help thread discusses a unique issue to a few niche sites that have no choice but to block all users from the United States while also wanting to allow GoogleBot to access the site.
Since GoogleBot lives in the US, blocking US based IP addresses, would likely also block GoogleBot. That would result in Google not indexing your site and you not ranking well in Google for the country you are targeting.
Googler, JohnMu, shares one acceptable way to block US based users but at the same time, allow GoogleBot to access your site. I assume this is not considered JavaScript cloaking, cause John said you can use it.
One potential solution would be to use a JavaScript-based interstitial that verifies the IP address and otherwise blocks access to your site. I assume you have to use JavaScript within your site, correct? If so, there would be no simple way for a user to selectively block the JavaScript interstitial and allow the JavaScript casino content. Assuming the JavaScript is in an external file that is disalllowed through your robots.txt file, Googlebot would not be able to view the interstitial and would be able to crawl the site normally.
This solution isn't necessarily new, but it is the first time I have seen a Googler suggest it in a forum.
Forum discussion at Google Webmaster Help.
