I just spent a few hours working on making a better print.css file for the Archdiocese of St. Louis' website, and, imho, it was time very well spent.
In a meeting just last week with the St. Louis Review staff, I noticed that three different people on staff had printed out pages from archstl.org, and those printed pages looked like junk. I had neglected spending much time with the Archdiocese's print styling (in a print.css file) when I originally designed the site, and I decided it was time to work on it a bit.
I first hid all non-essential elements (graphics, search, navigation, sidebars), then worked on styling the main body of the page a lot nicer. Now, it prints relatively well across Safari, Chrome, FireFox, and Internet Explorer. However, there's a weird bug in FireFox that causes some pages to print with a blank leading page, then with cut-off content on the second page.
At least it looks pretty :)
I think you'd be surprised how many people print out articles and pages from your website—especially if your site is heavy on written content. It's a good idea to cater to them just as you would to mobile readers and those using less-than-ideal browsers (<cough>IE</cough>).