Since I couldn't find a thread like this, I decided to make one.
How did you end up with your current team in Diamond or Pearl (or Platinum or both or all the three of them if you wish)?
Did you just catch your Pokémon on impulse? Had you planned catching them beforehand? Did you breed them yourselves? Or did you maybe trade them for some other Pokémon?
Why do you keep them in your team? Do they have nicknames?
I actually planned my team beforehand. I ordered my Diamond from USA so I had to wait a week or so for it to arrive. Because I had time, I started to find out what kind of Pokémon I could get. I decided to take Piplup as my starter, then catch a Starly and a Budew and later on a Ponyta, a Pachirisu, a Pikachu...
It didn't go as I planned.
I never even tried to catch a Pachirisu.
I ended up catching a Shinx. I gave it the nickname Shin (my Piplup was named Piyon) and decided to use it as my temporary electric type... Now it's a Luxray and I still use it, it's my best and my favourite Pokémon!
I did catch a Budew (it's a male called Brose and it's Roserade now), but it's really good only against Pokémon that have a weakness for grass. I love its Giga Drain, though.
I also did catch a Starly, but man, I hated it! At first I didn't even nickname it, it was only to be my slave using Fly. Somewhere half trough the game I realized that Staraptor is actually quite useable Pokémon. I nicknamed it Starrie and it's now as important in my team as every other Pokémon.
After those I caught a Geodude. I've always disliked rock types, so I didn't care much for my Geodude either. I still don't, but I use it occasionally. Three of its four moves are TM's, but the fourth one is Earthquake

It's called Gemmer and when I need room in my party, it's the first one to go.
Ponyta was my sixth Pokémon just as I had intended. I taught it Fire Blast as soon as I could and I've then increased PP to be 7. The Pokémon's name is Radeem (the name is from my fanfic... my Rapidash is a male, though) and it was invaluable when beating the E4.
I'm currently trying to breed a Pichu to be my new team member. I'm also trying to get my little Eevee (Renian) to become an Espeon, because as you noticed, my team is lacking a psychic type.
So, share the story of your team! How did your Pokémon end up with you?