This is good info for the weather hobbiest's back pocket. I would like to indicate two things that should be remembered when using this though...

As Danial Pointed Out, the "clock starts ticking" in his formula when the storm reaches 75MPH. This is very important for a best estimate. For example, Wilma did not become a hurricane until she reached a pressure of about 977 mb. This low pressure was a function of the overall surrounding environment, which also had a very low pressure. The lowest pressure for Wilma was around 882 mb. If you initialized Wilma as a hurricane at 1000MB (Wich is not correct, remember it was 977mb), you would get a wind speed of roughly 193 mph. When initiallizing at 977mb, which is the correct pressure, the wind speed would 170mph...which is pretty close to the actual maximum sustained winds (which were around 175mph).

Also important to remember is that this is an estimate, not a perfect science. In addition, the equation does not have an adjustment factor for strengthening or weakening hurricanes...with particular emphasis on weakening storms. The pressure in a weakening storm is not very representative of it's actual maximum wind potential. An example would be Katrina prior to landfall, the maximum wind speeds decelerated much faster than the pressure rise. This is similar to most weakening storms, so the 1:1, Pressure:Wind convention will not work for weakening systems. But this is a pretty cool little tool for hurricanes otherwise.