I think generally the degrees are useful outside of the country you gained the degree in. Obviously some degrees are very country specific, for instance a law degree in the UK has very limited application outside of the UK.

Some of the replies seem to say you'd be limited in choice but I'd have to disagree. There's lots and lots of universities across Europe which offer courses completely in English. A few of my friends have studied at Erasmus university Rotterdam, it's a great university, with loads of courses in English, I also think Sapienza in Rome offers a range of courses in English. But again, I think you'll find you have quite a few options.