I have my own personal triage mechanism for determining how quickly I get back to inbound requests. First, I call back people I know. There's no substitute for personal relationships in business - a fact that makes me lament my disdain for "networking." Second are the companies I have heard of/ want to work with. In my mind there are three primary ways a company can benefit from a business development deal: cash, PR/ branding and future opportunities. Even if the cash isn't there right away, doing a deal with a well known company is always good as, at the very least, you can draft some PR off of their name.
Third on the call back list are the companies where (a) I don't know the person emailing/ calling me and (b) I'm not familiar with the company. With this group, sometimes its just a matter of my schedule, other times it's after reading their email/ looking at their website, of whether it makes sense to get in touch with them.
But on occasion I admit that at times make that decision based on their area code. What do I mean by that? Take for example if I get a "cold call/email" from someone I don't know who wants to chat with me about their ad network. There are lots of ad networks out there, and I'm always interested in learning more about them. With that, I will look at whether the person has a US area code in NY, LA, SF or Chicago. If they don't, they fall down the triage ladder. My presumption is that, based on their location, their product won't be that interesting. Kind of crap, I know - especially from a Pittsburgh guy.