I don't think I'd given any conscious thought to the nature of search within a SharePoint environment prior to attending the first offering of Bob Mixon's Findability webinar series. In that webinar, Mixon mentioned that most users tend to search on the Internet, but resort to browsing (i.e., point and click) on intranets. Mixon went on to say that, once thousands of sites/documents exist within an intranet, however, search becomes essential in the intranet environment as well.
(By the way, if you'll kindly permit a brief promotional aside, we just launched a new Bamboo Nation property this morning called Spotlighting the Rock Stars of SharePoint, and I was pleased to interview none other than Bob Mixon for our debut feature interview in the series.)
Needless to say, there was clearly much wisdom in Mixon's observation, so I paid particular attention during the search portion of the Mindsharp Power End User training I attended last week. One of the things I learned is that the search dropdown is configurable. As you can see, the default at the top level of our corporate portal is to search the entire site (including all sub-sites, that is), but that dropdown could include each individual team's sub-site as well if such were desired.

The advanced search hyperlink will naturally provide you with the means to narrow down what you're searching for, even limiting to a specific language, which is a pretty cool out-of-the-box feature, I must say. In addition to the default "All Results," the "Result type" dropdown includes options for Documents, Word Documents, Excel documents, and Presentations.
In conclusion, I'll leave you with a few tips from Mindsharp on increasing the likelihood of success with your searches:
- Check spelling;
- Use words, phrases, and sentences;
- Use similar words;
- Use more words;
- Use precise words;
- Use quotation marks; and
- Use advanced search.
Needless to say, these search tips needn't be restricted to searching on SharePoint sites!