Having already started the journey...
Well, we Oath Brothers are 2 years into our grand project, and are expecting to see print in two (er..maybe three) months... and I've got to say, its been a wonderful (although exhausting) experience.
We expected some sort of nightmare regarding the OGL and d20 license...someone to come along and say "No, you can't do this!" but we've gotten nothing but great responces the whole way. (If you're going with the d20 license, some (free

) legal advice doesn't hurt, either.)
Regarding using other people's OGC... yeah, we dropped them an e-mail. Why use their stuff? Why send a courtesy letter when the use of OGC material requires no notification?
1) Its a chance to say "hi" to them, as well as say "we like your stuff"
2) We want to give them credit. (Unless a person's just a jerk, who would want to pretend they wrote something that they didn't?)
3) Its a chance for them to get credit for it in a manner of their liking (i.e., "please tell us how you would like to be credited").
4) Not crediting someone would piss them off. Not discussing OGC concerns, no legal action, just peeved. (And what non-jerk wants that, either?)
5) Its just the right thing to do. You'd want someone to drop you a line and tell you if they were reprinting
YOUR OGC material, wouldn't you?
The responses we got to our friendly letters were encouraging, and its a little mindblowing to correspond with the "game designer iconics" (such as the gracious Monte Cook).
As for crunchy vs creamy, that's where my OGC versus non-OGC alligences lie.
The beloved "crunchy" parts (spells, monsters, prestige classes) make for great OGC, especially when they can be used universally.
The "creamy" parts (campaign setting, NPCs, pantheons) make for good non-OGC Product Identity.
One final note....from your previous post:
Fourth, that community should create a trade organization (where size doesn't matter) to help the members with legal, marketing, and production issues, etc.
Interesting idea. In some ways, Natural 20 Press does some of this already, esp. with marketing and production issues for small publishers. The idea of a size-doesn't-matter trade organization seems flawed, though. Why would a larger publisher put their legal and marketing resources at a group's disposal?
On the other hand, some sort of private board for publishers to chat with one another off-the-record would be wonderful. Almost like a d20 publisher mentoring program. (This would be ideal for the smaller publishers, not the more competative larger publishers.)
The road to publication is great. If you're serious about putting something out, stop worrying about the nitty-gritty of the OGC (you're overcomplicating things) and go for it!
Will "Liu Bei" Russell
Oath Brothers
(Consider this the words of the Oath Brothers!

)