I just discovered that Drive Thru RPG (and presumably RPGNow) offer POD. What is their quality like?
My experience for their POD service was that the quality was equivalent to Lulu, in both hardcover and softcover deliveries.
The hardcover projects I received were case-bound and not stitched, but the paper quality was good (slightly better than with paperback releases). Anecdotal experience has led me to feel that this method of glue-binding hardcover books (in general, not just from POD outlets) works best with sizes somewhere between 120 and 240 pages: books with fewer pages, or more pages, seem much more prone to spine cracking and pages falling out, so if you're thinking of a small-page count book, or a very large one, then you might lean towards the softcover option instead.
The softcovers I received were perfect-bound and well done; the only quibble I've had with the softcover products (and I've had the same complaint with Lulu) is that the method of printing and cutting the covers leaves it quite easy for the plastic laminate that lies on the cover to start peeling back from the cut edges of the cover (once this happens, it's next to impossible to really do anything about it).
Lulu and RPGNow share the same printer, Lightning Source, within the United States. If there is a difference it is because Lulu's ability to process a PDF is better than RPGNow's. A correctly formatted PDF, a PDF saved using PDFX1/a format, will print the same on both. But Lulu has fewer pitfalls in their setup so the chance that a given author has a correctly formatted PDF are a little higher.
However, while print quality may be an issue, issues with the author/publishers dwarf the differences between the print quality of the two companies. Like all print on demand, you need to check out the feedback and the reputation of the author if you want to be sure of the quality of your purchase.