When visitors click this print button, they get an option to pick and choose the blog posts they want to print, and skip those they don't. Only the text and images are included, everything else including advertising, header graphics, sidebars, etc are stripped off.
The blog posts are then saved as a PDF files in A4 or Letter format on the reader's hard-drive. For sites that do not offer RSS feeds, HP will offer a separate Print widget next month (based on Tabblo) that will allow site owners to add print functionality into their existing websites.
The HP Print Widget is currently being tested on popular blogs like Dooce, TechCrunch, BoingBoing and may become widely available sometime next month. [Until then, you can consider making your website printer friendly with simple CSS]
Overall, a very elegant print solution that will also help save trees since your reader are saved from printing non-essential webpage elements.. Expect to see the HP print widget on majority of blogs in the coming weeks. [Thanks Nathan]