because of problems that are not mine but I was involved - I did research, using looking glasses tools on many ISP all over the world. Seems (it is possible) that the II (and not only - thepiratebay for example) are banned. For all ISPs in Italy all routes get via networklayer.com So, it is banned or that US ISP have problem. *ALL* of Italian ISPs get via networklayer.com - so no one Italian can view II.
Do not know about other countries, in my I've found ISPs that are OK getting II, and other that have *same* problem - route to that networklayer.com and no II!
Finally I am not sure is it banned or just one main US ISP have problems...
Workaround paths are to get service (free or payed) for proxy usage or just tunneling (btw it is almost the same).
One of the best free solution I've found is http://www.snapfiles.com/downloads/ultrasurf/dlultrasurf.html
Another (but every one must try it) very good fast solution is using google translator - BUT if all country has problems connecting to II , the translator will has too - because google use locally (even physical) servers.
There are of course many free proxies too...
ok, sorry for my English
hope it will helps to someone needed that info