I used them on Diamond and Platinum, but only for Wi-Fi battles. I wanted to make a scene while having my Pokemon enter battle, but that was it really.
I would have used them if they were more available in HeartGold :shrug:
You get, like, 3 random "items" a day and it takes a while (just based off the three days of getting them ) to get a good collection going.
But basically all it is, is you have these "decals" or pieces, and you can place them on a specific Pokemon (it comes in a form of decorating a PokeBall pretty much) and then whenever that Pokemon comes out into battle, those specific decals/seals used will pop out with the Pokemon.
So you can have obscenities pop out as well such as "f**" or "J00" when throwing out your Poke named Snowy. Assuming you would name a Pokemon "Snowy", and only the "J00"applies, f** can be saved for whoever you want Big Boi~ :-*