will that make it so American users like DT, trachy, PB-10, J98, Swampert etc. will not be able to use the site?
Basically, yes. The chance of it affecting us isn't huge, but the point is anyone could make a copyright claim against us for a link or image posted on the site, and we would get blocked in America.
wouldn't it be illegal for them to block a site from another country that would even violate their own amendments
I believe SOPA is mainly targeted towards blocking sites in other countries. The site doesn't get shut down, but American ISPs would have to block access to our domain. Which is exactly why this legislation is a complete load of crap as it wouldn't stop piracy anyway.
Would this effect users from other countries like Canada?
I'm pretty sure it wouldn't affect Canada and it wouldn't affect other countries directly. But if the bill is passed it sets a precedent for other countries to make their own similar laws.
You may have noticed that some sites like Wikipedia have completely blacked out today. I thought it would be useful to add a banner to inform more people about it... although most people here are probably below voting age ;)
PS out of interest, had you heard about SOPA/PIPA before today?