Finally! Google Print is now starting to produce results for works in the public domain (but it appears to be working only through Google.com and not co.uk). I googled Oliver Twist and got the entire book in the results (TIP: It is the icon with the books beside the link). I also was able to find The Count of Monte Cristo and Dracula.
But beware, the service is still in BETA, so most of the books are available as placeholder and provide a few pages and the table of contents. Still, this is a very exciting development, and it could prove to be a very good marketing tool for your writers, as you are allowed to advertise your own book with Google Print.