Hey Nate,
I bought my car with the bolt broken and didn't know it. Do not run your car with it broken. I would get it fixed ASAP. I had complications due to that broken mount that ran into the thousands. When it breaks, the transmission + engine sits directly on the subframe. If you look in the drivers side wheel well, you will see this. The tranny should sit an inch or more above the subframe. As a result of being left for so long, it damaged my control arms, allignment, tires, tie rods, etc etc etc. I also had crazy vibrations in the cabin because the engine was no longer insultated from the chasis. Once i realized the problem, i bought the new bolt from Ford for $50 if i remember. You might need a special too to get the bolt in correctly though.
Bottom line, get it replaced ASAP and check it from time to time to save any long term problems.
Nate