This is a dynamic version of the search engine that uses Google Ajax Search API.
Advantages: With Ajax it's easier and faster to search. Also, this version displays books available on Google Book that can be viewed or completely downloaded ("full text" books). This is not possible when using the normal version of the search engine.
Disadvantages: Visitors from countries where legislation regarding intellectual property is more restrictive cannot download copies of some "full text" books that appear in the results of a Google Book search.
Furthermore, clicking on the "more results" link will open a new window, something that may inconvenience some users (one of the limitations of "Google Ajax Search API").