A vbulletin genius recently helped with our server migration and server optimizations to this new server. I've asked him for his thoughts on a viable way to interlink the two forums (APUG & DPUG). The ideal solution is that everyone has one user name, one profile, one "new posts", etc and can use both sites seamlessly. vBulletin 4.2 is out and may have better back end tools to accomplish this.