I've actually heard that the people in Amsterdam are fairly friendly to Americans (assuming you're in a tourist-y place).

The Cannabis Cup takes place in November, I believe. Either that or late October.

As for places to visit, try this--http://www.amsterdam.info/coffeeshops/

I'm planning on going this winter. Probably sometime around early December. We have a good month off from school (Oh, the joys of college) so I'd be looking to stay a good two weeks minimum! I cannot wait. It's going to be amazing.