Terence Tao: I recently discovered a CSS hack which automatically makes wordpress pages friendlier to print (stripping out the sidebar and header), and installed it on this blog (in response to an emailed suggestion). There should be no visible changes unless you “print preview” the page.
Being a print-it-out kind of person, I ran into the "weblogs (or other web pages) not printing properly" problem way too often. Typical problems are: i) words being cut off on the right hand side; ii) only one page of real content is printed (example: Neal Gafter's blog).
I hope that someone can take the idea from the above link and make it work with other blogging engines/providers. It doesn't look very hard. (Pebble, the engine behind this blog, already uses a separate stylesheet for printing.)