I use Google as my base, optimize the various Places/Local accounts, and let the SEO gods do their work. I find that if I really only concern myself with Google ranking, Bing/Yahoo reflect it as well. Case in point, the keywords/cities for a project I've been paying extra attention to (I've talked about it here over the last couple of months), have Google rankings of 1 or 2. In Bing and Yahoo, I just looked and some of those same keywords actually tend to be ranked 1 AND 2 (specific sub-page is always first, with the root domain link ranking second).
a guy who knows both the lawn business and web strategy