Google has just souped up its ability to 'teleport' you to the exact website you want, even if you just type in its generic name without the appropriate .com or .net ending. Now it has added a supplementary search box which will crop up in the search results for the site you're looking for.
The writeup on the Official Google Blog gives the example of searching for "NASA" when you're looking for information about the Hubble telescope. The search result for NASA pops up a few NASA specific links, followed by the "search within the site" search box (as pictured above).
This secondary search box won't appear for every search, however. Google hasn't said which sites will get the 'search withiin the site' box - it's down to Google's secret algorithymic sauce, apparently. "This feature will now occur when we detect a high probability that a user wants more refined search results within a specific site," reads the blog post.
Search within a site - a tale of teleportation [Official Google Blog]