We’re not big printers, but our customers tell us they are. They often have to print screens from Basecamp to take to meetings, present to clients, or prepare a report for their superiors.
That summary hits the key message for me: you (the website author) may not print much from the web, but if some of your readers do, they will really appreciate this support. Having well-designed print stylesheets is a sign to me that the authors and designers care about the user experience to put in these details.
I’d really like to convince the major blogging software and service vendors to add print stylesheets as part of their default packages. I’m about to update to the latest Movable Type, so maybe I’ll fire up that evangelism effort again.