Hiyas
I dont think many decks play Stump at the moment, and I dont think ANY decks I know of play 4 of them. Battle Frontier and Desert Ruins just offer so much more in todays environment than Giant Stump does. Having 4 pokemon in play is quite a lot, and most decks dont need more than 4 pokemon out for their strategy to work.
I can see it being annoying in certain situations though. For example if your opponent has 6 pokemon in play, use Stump, and then grab a KO, and they're suddenly down to 3 (although some of their strong pokemon will probably still be alive). Also, playing it so your opponent can't play splashable basics (eg. Lugia ex or Mewtwo d); and of course, healing your own pokemon.
It's a useful card, that could work wonders when used properly, but if you're going into a tournament, I'd be surprised if you saw a lot of Giant Stumps played. I think Ruins and Frontier are the gyms of choice at the moment for most decks.
~Secretsmeargle