Orgs are great for forums (general rule of thumb; anything that involves 'people' can adequately utilize a .org. Anything that involves "products" is best suited by a .com)
The .com instinct is pretty much reserved for offline marketing, where people are going to hear/read your name in some form of media, then have to remember it. Further, if it isn't competing development (you're trying to do something on the .org that overlays with similar development on a .com), your minimal traffic bleed will most likely bounce back anyway once they wind up on a PPC lander, realize "oh, yeah... .org, not .com" and navigate to the right spot. Further-further, if the .com is undeveloped, now's the time to act. SE age/trust is critical for an entirely web based concern, yet hilariously neglected by 'domainers' who horde names and never bother to do anything with them.