Do you plan out your campaigns or just fly by the seat of your pants? Do you use McGuffins?

When first starting a game, you normally will sit down and maybe get an idea of what you want to do, but do you plan things out? or do you wing it by the seat of your pants?

I know I personally like to sit down and hammer out some of the background, the rules and the set up of the story along with the names of the key NPCs. I may or may not write down the focal point of the story, the "McGuffin" of the story if you will.

From here, I will just run with the campaign, taking it session by session, always reacting to what the players do with their characters.

Based upon this information, I will jot down a note on a sticky so I remember it or write it in a DM Journal, so I know next session, I want to branch off of this and it worked really well.

What say you?