I once read a blog entry (I think from Laurel K. Hamilton?), who suggested that instead of fact-checking as you draft a manuscript, you should leave spaces as you write, then confirm the things you had questions about later on.  The idea, of course, is to allow yourself uninterrupted time to write without constant fact-checking.
It's a nice idea, but I'm generally too distracted by potentially incorrect facts to leave them be.  (And that's partly the price, I think, of having wireless internet ac