As reported by Stargazer's World, RPGNow/DriveThruRPG will soon begin offering Print-On-Demand services as a complement to their current pdf sales.
If Michael's example in his article stands up, it sounds like shipping might be reasonable. If that's the case, the make-or-break for me will be a) customer service, an area that's been hit-and-miss for their biggest rival in this field (lulu.com), and b) print quality.
I really think those items, along with effective shipping, are going to drive how successful this is. Otherwise, I think we'll see a definite boon to small-press publishers, many of who will be able to push their print products a bit more easily from the largest RPG pdf store out there. It's a pain to take a pdf to places like Kinko's or Staples, where often they will refuse to print a book for some fear of copyright violation or somesuch. Lulu.com allows you to upload files for printing, but as alluded to before, it's hit and miss as far as what you get with them. We'll see how this works out.