reading your reports

I am trying to fully understand the reports generated by S3Stat. Here is were I am a little lost.

While I see a link for Countries on the report.
http://playbacknar.com.s3.amazonaws.com/stats/usage_201105.html
It does not display any country information. Should it?

What does Hits by Response Code mean? See below, also on the report URL listed above.

Hits by Response Code
Code 200 - OK 10254
Code 206 - Partial Content 37
Code 304 - Not Modified 11
Code 404 - Not Found 2

Finally what does User Agents mean? Near the bottom of the report.