CVG reports that stickers will play a prominent part in upgrading your characters in Super Smash Bros. Brawl, the official website revealed today. It might be worth re-reading that sentence to make sure you didn't just make it up in your head.
You can pick up stickers throughout the game and each sticker houses a special power up. Usually the bigger the sticker is, the more dramatic the power-up will be.
To benefit from these power-ups, you must paste the stickers to the bottom of your trophy base, but it only has limited space for a finite amount of stickers. It sounds like yet another RPG advancement system in a colourful and playful disguise.
Unfortunately, stickers can only be used within the single-player mode The Subspace Emissary and will have no use in standard brawls.