Why Belgians join AOPA US...
I think the $60-odd annual fee is for overseas members, as opposed to $40-odd for US residents.
I joined AOPA US because my main certificate is FAA and because I fly in the US from time to time. I also like their views and explanations as regards GA advocacy (e.g. how to convince the neighbours that GA is a good thing), their training materials, their reports on adventure flying accross the world, their accident investigations, their "Never Again"-stories, the legal opinions and, not in the least, the ever humourous contributions of flight training guru Rod Machado. Everyone - at least for the moment still - is free to do with their money what they want.
I didn't join IAOPA Belgium because it was (virtually) non-existent. I notice from patowalker's reference that they still operate, which is obviously a good thing. It might be a good idea to give them a call : Finserve is, if I'm not mistaken, an aviation insurance broker based at EBAW. By talking to them, you quickly know whether there is a match with your own feelings towards GA and whether they have any significance (e.g. would they advocate improvements to EBGB, are they lobbying the Belgian BdL to reduce costs, what are they doing about the lack of proper (night) training airfields in Belgium, do they have a Etienne Schoupe's or Joke Schauwvliege's mobile, etc, etc...). Please report with feed back, I'm sure the Belgians on this forum would be interested.
I have mixed feelings about the various IAOPA's across Europe. They certainly deserve some slack, doing a lot of good work on an almost purely voluntary basis, not being able to benefit from a 400,000 strong membership and $100 Million balance sheet like AOPA US. On the other hand, they have been a bit quick to claim credit in this EASA-story (or in the Italian case cited above, about the fuel situation on Italy's regional airfields), without a lot to substantiate for. This in contrast to an AOPA US, which lists several politicians and their stance on general aviation and who (up until now) has rebutted all attempts at introducing user fees into the FAA's budget. But again, life is easier when you have reams of permanent staff at your disposal, which the European IAOPA's have not.
I stand corrected on DUAT(S). I recall joining them while clicking through from the AOPA website (I think in the AOPA flight planner), and although they advertise regularly in AOPA magazine, they are most likely completely independent. And yes, they are only useful when flight planning in the US.