Joking aside, including Craigslist in the list of places from which you pull your potential users doesn't sound professional to me, especially in a list with others like LinkedIn; It makes the service sound like a web crawler that hits into lots of noise while trying to classify users.
That being said, we're pretty agnostic to the methods we use to source our leads. We find that different industries can have widely different lead generation methods that are most effective. The advantage to our service is that we can customize how we generate these leads. If Craigslist ends up being the best way, we'll use that, if it's a different method (LinkedIn for example) we'll use that method or any other method that works well.