As Rudi said, the search engine on Epinions has been a weak spot for several years, and many of us have also made the same Google suggestion. In one such discussion (at least three years ago), someone from Epinions said that it costs them to use Google's search engine on the site, and that's why the site has its own home-made search.
Yes, using Google's search would be easy, but it costs more. And that's what we have been struggling with for years. You don't have to tell me about how much less frustrating a Google search tool would be -- almost all of us were convinced of that years ago.