I haven't really given this much thought before now. However, I was playing around with some of the items in the Safari Extensions Gallery and found an automatic currency converter. So comparing the prices in the UK store and then the converted prices in the US store, the difference on a base Mac Pro is about £300!! Would it be a good idea to import a machine from the US store? My guess us that the power supply should work OK and would only need a different shaped plug on it - how much of my £300 saving would I realistically see?