Living in Chicago, I own a mountain bike but I can't exactly say that I mountain bike. That said I do think my road bike handling skills have improved, but the biggest improvement I saw after I started trail riding more is that my cadence and pedal stroke improved greatly, riding in the mud and up hills, especially muddy runs, helps you increase your cadence but at the same time forces you to keep a nice rhythm so you don't just end up spinning your rear wheel all over the place.