In the customer profile, it is annoying to have to select the option for where a customer is VAT registered based (ie. home country, the EU, outside the EU etc).
This should default to the country used for the billing address - as surely that is where they are going to be based!
At the moment, it always defaults to the home country, which means I often have to look up to see if a given country is part of the EU or not and remember to change this flag, which can lead to mistakes.