There are many reasons to convert that aren't simply because everyone else is.
The US is effectively in a state of operating with dual measurement systems, and that is costing your economy significantly. Various industries need to keep and maintain two different sets of tools with different measurements, many industries use a confusing mix of both units. e.g. The electronics industry is a big mess, with internationally acquired components being specified in metric, while PCB design and manufaction in the US is done in imperial. Internationally, everything is done in metric.
Your roads are designed in Ramsden's chain (100 US survey feet), with long distance measurements being done with GPS in metres and then converted.
NASA has fucked up so many times, by living in a hybrid world of both systems, rather than actually properly committing to change.
Your continued use of non-metric units in the health industry risks lives due to doing calculations with the wrong units. e.g. calculating how much medication to prescribe and accidentally using lbs instead of kg. Or using non-standard symbols for metric units, such as MG for milligram (which should be mg) and MCG for microgram,which should be ug (slashdot won't let me enter the proper micro sign) More info on these problems here. http://themetricmaven.com/?p=67
Ultimately, this hybrid system costs your economy more because you cannot effectively work the the same set of tools that everyone else can. It affects your education system because kids must learn two systems, and yet when learning metric, have very little reinforcement in the home due to many consumer products being labelled in USC or both systems, with comparitively few labelled in exclusively metric. I think wine bottles are one of the few products that aren't labelled in both systems.