Reprinting of OGC...
I think there is a fine line to walk here... re-print OGC and incur the wrath of those who already own the source. Don't re-print it and incur the wrath of those who don't (and don't want to have to spend extra money).
Here are my thoughts...
As has already been stated, modules ("adventures" for the non-grognards among us) offer most conducive setting for re-use of OGC in the form of Monsters, Spells, Traps, etc. I have to agree that the market is somewhat limited, though... there are only so many modules for 1st-level characters you can use before you are dealing with 2nd and 3rd level characters... ;-)
As far as "sourcebooks" go, I think that there IS room to include reprints in a sourcebook... provided you are very selective about the way you do it. While nobody wants to see that 32 pages of a 64 page sourcebook consist of reprinted OGC, I don't think people mind if you include 5-10 pages of OGC (a piece here and a piece there) for completeness.
Now, admittedly, I am the publisher of one lone d20 sourcebook in PDF format only -- I am NOT a big-time publisher -- but I concentrated my sourcebook (The Enchiridion of Mystic Music) on bards and music. I wanted to make the book completely self-contained (that is, requiring only the Core Rulebooks for use) and to do that, did not feel bad about including a snippet of OGC here as reprinted OGC. I believe the PDF is 74 pages (about 70 pages if you remove the cover and the OGL/d20STL from the equation) and I would venture to say that the amount of reprinted material is just about right for my goals... I spent 2 pages on a re-print of the bard class (with minor variations), 2 pages reprinting a prestige class (also with minor variations), 1 page reprinting spells, and probably another page or so reprinting snippets from other sources.
In total, the reprinted OGC represented less than 10% of my work, and only the 1 page of spells was reprinted without making changes in order to work it into my book (so 1 page of "complete reprint" as opposed to "reworked" stuff). I have not received any complaints asking "why did you reprint this?"
I would venture to say that provided that you stick to your focus, you can bring in little pieces of OGC "from the outside" and reprint them without worry of people complaining... when they note that you're not including tons of material, but have chosen very carefully only those precise pieces that are absolutely necessary to add to the new and original material in your book in order to allow your product to be more or less of the stand-alone variety, they don't complain. I never had a problem with that as a consumer, and I figure if I didn't have a problem with it as a consumer, I should assume that I could do it as a publisher.
I hope most readers will understand that... they understand that you're trying to save them the trouble of buying another book (or referencing it if they already have it) but at the same time, not trying to make them pay twice for the same material. If that's the goal you have as a publisher, I think it will come through in your publication. OTOH, if you do have the goal of making people pay twice for the same thing, that will come through, too.
Flame away here or send an e-mail to me...
the_sigil@hotmail.com
--The Sigil