The IP address is the best kind of unique identifier it has for a non-registered user. If someone's registered, then it shows their user name, but otherwise the IP acts as the unique identifier. I agree that this isn't all that useful, but you can use it with services likehttp://ip-lookup.net/ to figure out more about where they're from. That IP is used by the stats app to determine the country of the user (where possible). I might be adding some more detailed location info based on that IP address in later versions.

A site visit is when someone comes to your site. If they visit 1 page or 20 pages it still counts as just one site visit. A page view is how many pages are opened.

Timed out means that the user opened a page and just let it sit there for a long time, and the stats system was never notified that the page was closed, so it's assumed that the visit ended. It can't say how long he visited the last page he was on for this reason. The default timeout period is 20 minutes of inactivity.