For a while I was ranking quite well for a keyword across all of Google, but then about a little less then a year the site disappeared off of Google and only ranked for the keyword on the US version of Google, and countries that used the same datacenter as the US version. But finally, couldn't have been less then a week or more ago - my site now appears within the first page for all North American versions of Google (ok maybe not all of North America -there's like 23 countries technically, but US and Canada at least)
It is always a up and down game with Google Search Results. That means your competitors are not sleeping and you have to work hard to be on top.