According to the website, rollyo allows you to create a search to sites which you already know and trust. Basically, rollyo enables a user to pick the sites that the user wants to search.
I have created a rollyo search here in this blog. On the right column, there is a text area just under "Search my blogs". If you type in a search term and click [go], rollyo will produce a result based on seaching my blogs only.
This can be very useful for creating customised "resources" in education sites for the minors. At the moment, rollyo limits the number of sites to be searched to 25. This is probably not enough.