I have been working on a few horizontal products and the starting challenge with chicken and egg is always the same - you need to attract one vertical community and allow to fill it with content.
What kind of strategies do other people use here? We tried automated import of existing content (e.g. from a publisher), paying people to generate content (with a set of rapid authoring tools). These strategies fill up content, but they don't engage a community and don't engage users to share content. Another strategy is to engage a lead user who already has a following, but this distorts the product into an individual one.