Gasoline blended with ethanol can suffer from phase separation when the temperature drops (the ethanol 'unmixes' itself from the gasoline). Ethanol is also hygroscopic, which means it has a tendency to absorb water. If the ethanol separates from the gasoline, it takes the water with it and tends to form an emulsion at the lowest spot in the fuel system (the water / ethanol mix having a higher specific gravity than the gasoline). If the fuel pump sucks up a slug of this emulsion, it has less heating value than gasoline (higher water content will make it worse) and you will definitely notice poor engine operation. Note that phase separation usually occurs when there is a temperature drop; however, given enough time and enough moisture in the gas, I am going to guess that you can incur phase separation even without a significant temperature drop. Once the ethanol (and water) separates, it tends to stay separated. If the gasoline and ethanol is shaken or mixed up (this can occur when adding new fuel) the ethanol may form a brief suspended emulsion with the gasoline and you may eventually get rid of it this way.
The fuel stabilizers that I am aware of seem to deal with deterioration (gumming) of the fuel as it ages. I am not aware of any fuel stabilizers that prevent phase separation.
In western Canada, premium fuels are usually blended without ethanol, which reduces the phase separation problem. You can still accumulate moisture in (non ethanol blended) gas which will separate and accumulate in low spots; but, with the sealed evap system on the NSX, that should be a pretty low probability event.
