Custom search engines

Techcrunch had an article recently about the various things being done at Google. One is a Rollyo-type custom search engine which will allow you to restrict your search to a few sites of your choice. I liked the idea of Rollyo very much but couldn’t get to use it as the base search engine is Yahoo’s. It would be great if Google had two versions - one based on the regular Google search engine & the other on Google Blog Search engine.