One of the things you will notice if you go to Estonia is that there is a lot of prejudice against the Russians living there. Not surprising, considering Estonia's recent history, but it's something to be careful of. If you speak Russian, you have a good chance of being understood, but you have an even better chance of being resented.
Americans are treated very well in Estonia. I found myself in a lot of conversations because the locals wanted to know what life was like in America, whether I thought Tallinn was cheap or expensive (it's very very economical), and why I decided to come to Estonia. I think all North Americans and Western Europeans will likely receive this treatment. Most Estonians in Tallinn speak a decent amount of English, and those in the jobs related to tourism speak very good English. Outside of Tallinn you might have to work to make yourself understood.
Overall, I found the Estonians extremely nice people. Cultured, curious, and friendly, if a bit reserved. It seems like they're rushing to catch up with the world after being held-back during the Soviet years.