It may be most advantageous to do one facebook for the following reason: Lets say someone get 5000 fans. Lets say those 5000 people each has 100 friends, so now your reach is to half a million people on the social graph. By keeping your social reach coming from one source, you drastically increase the odds of having a like from someone your potential customer knows by association, which is a big plus in search and in selling, since there is a personal recommendation.
Moreover, getting your fans locally makes sense for local customers. Becoming a community name is a sensible strategy for a local grocery, clothing store, eatery or other small business looking to establish a web presence. By having one facebook, you increase the geo-relevance of your business, which are important social signals search engines likely use, and definitely will soon.
There are other things you can do to establish geo-relevance. You can build landing pages on your business facebook for your other areas, and have visitors from that local area direct to this page. But it should be all in one well branded account. By using a second page, you are diluting the brand somewhat.