I was heavily into the game, mostly because I could spike the tournaments filled with 8-10 year olds (I was 12), and used the prize money to fund my Magic: The Gathering hobby.
The trick was that kids would go Gaga over foil cards, and treat regular cards like dirt compared to them. I could trade borderline useless foils like Clefairy and get all the Pokemon Breeders, Computer Searches, and Electbuzzes I could ever use, and this only got better when Jungle and Fossil came out, because all the foils were just shiny versions of the normal rare cards, so I could get playsets of Scythers and other great cards pretty easily by targeting non-foil versions.
I was pretty much done by the time Gym came out in English. People actually got better at the game, and the tournaments around here had started becoming much lower stakes (spreading out prize support so that most players got -something- instead of top-loaded), so it didn't make much sense for me to continue playing the game anymore. I sat on my cards for about another year, before trading them all to my brother in exchange for him letting me pick 2 PS2 games I wanted (There was a B2G1 free at Toys R Us, and my parents decided to let each of us get a game we wanted, and 1 to share for free as a reward for something, so I gave him the cards to make him choose Final Fantasy X as his game, and to pick VF4 as our "shared" game).
I don't really know much more about the game past Gym 2, but I know that it has made some drastic changes- Basic pokemon now have hundreds of HP, trainer cards are weaker/more restricted, ect.
