Google has deprecated their SOAP Search API. This means that people who already have keys to use the system can continue to do so but no new ones will be issued. Ongoing support of the SOAP API is questionable as well. Google suggests that people now use their AJAX Search API. Here is a good discussion (read comments and follow links) of concerns about how the AJAX API is not a complete replacement for everything that was available in the SOAP API.
Update: Here is another interesting post, Beginning of the end of for open web APIs?, that is worth checking out on this issue.