Searching in Safari 5.1
As you can see, you can choose between ”Contains” and “Starts With” and by default, the option selected is “Starts With.”
This menu and these options didn’t exist in Safari 5.0. It’s not exactly an obvious change, so I didn’t notice it.
I had also been caught by surprise at Safari being seemingly unable to find text within a Web page.
Update (2011-10-10): There’s a FindOnPageMatchesWordStartsOnly default.