Whilst I wouldn't normally care what scale another country uses, it does affect me because I watch films and television from the United States. For example, in Survivor Guatemala the host mentioned that it was 120 (or was it 110) Fahrenheit, so I had to get google to translate "120 f in c" as 49 degrees Celsius to realise that it really was hot. So, if only for the benefit of international relations, I believe the scale worldwide should be standardised. Although I imagine there'd be great resistance amongst the general population in the US, other countries have managed to switch seemingly without trouble.
Update (28 Jan 2006): John Quiggin has some interesting thoughts on the whole topic of why the USA has not gone metric:
the attitude underlying the adherence to traditional measures is that the US is rich enough and important enough to do what it likes, and the rest of the world can like it or lump it (an attitude not unique to this issue). There’s a lot of truth in this, and it helps to explain why the US is pretty much self-sufficient in a wide range of cultural services. On the other hand, it’s not conducive to success in export markets for goods.