Serendipity blog comes with an excellent search tool that allows users to find all posts that contain a certain word within your blog. As theme designers we need to be aware of how the quicksearch plugin works, and how to style the results appropriately.
At some time almost every users has noticed that the quicksearch tool doesn't work as expected, often because it can't find a result for a word the user knows to be in their entries. The quicksearch function relies heavily on the a similar php function, and a design feature of the quicksearch is that a word that appears in every post should not produce any results, after all what is the point simply reproducing the archives page.
To test the two different results that a user will experience, try searching for 'pluto' and 'column', now search for one of these words spelt incorrectly. If your theme is fully compatible with serendipity blog you should be happy with the results.