We thank Andy Fabian, David Garofalo, Julian Krolik, Cole Miller, and Andy Young for insightful and stimulating discussions throughout the course of this work. We also thanks the anonymous referee for their thoughtful comments which lead to a dramatic improvement in the presentation of Section 3.4. We gratefully acknowledges support from the National Science Foundation under grant AST0205990 (CSR), AST9876887 (MCB) and AST0307502 (MCB).