The situation in the Netherlands is more complicated. Technically it's still illegal, however it's effectively decriminalised for personal use. Small amounts found on you (less than 5 grams) will not be prosecuted. No more than 5 grams may be sold to one person in one transaction. You must be over 18. 'Coffee shops' should not cause any trouble, drugs may not be advertised and the mayor can order a 'coffee shop' to be shut down.
More recently (2012) these coffee shops have also been ordered to close their doors to foreigners, and there's a proposal to classify very potent (over 15% TCH) marijuana as hard drugs.
Things keep changing so who knows what will happen in the next few years.
Does the EU have the equivalent of "feds" in the USA (e.g. DEA) that could catch someone with small amounts of marijuana in the Netherlands and prosecute them not under national law, but under EU law?
Nope. EU doesn't do criminal things. EU tells countries what their criminal systems do. There is Europol (European Police Office) which is only for aiding cooperation between national police forces. It has no powers of arrest, and (most tellingly) it only has 800 staff for a population of half a billion people. Not at all like "the feds".
And I don't think there is any EU law on illegal drugs like that.
Yep. Netherlands is basically "It's illegal but we don't enforce it". Which I can understand. That's different from "It's illegal and legal". Which sounds crazy...
