Just on a lark I tried out creating a page for my business (BudgetSimple) on Facebook. The experience is very interesting. The concept is that instead of just providing a link you create a way to express their use of your product by "Becoming a fan" of your company. Facebook also offers a very simple "AdWords"-like way of advertising to the Facebook community, where they can not only visit your website, but also rate the quality of your ad or become a fan.
I have not had phenomenal success as yet with this form of advertising, but one thing that sets it apart from Google is the demographic data you receive. Unlike Google, Facebook knows every last detail about a person, including age, sex, etc... and provides you a rather nice breakdown of this. Of course it's probably skewed by the age generation that uses Facebook, but even my 60 year old father is on Facebook at this point so it's probably not that far off. Definitely worth a try if you are an mISV looking for new creative advertising routes.