I've made a customized Google search engine using sites I commonly use when compiling Friday 5 lists. It's now listed on the left-hand side of my blog along with a box that allows people to subscribe to the Friday 5 in Google Groups. If you ask to contribute to this search engine, you can add relevant sites. It is also possible to add the search engine to your blog, homepage, or Google start page.I can see teachers using Google Co-Op to make customized engines for various units of study. I think it's a pretty handy way to direct students research instead of just letting them loose on the Internet.