It looks like Valve is starting to really pour the same love and care into Counter-Strike: Global Offensive that it has continuously poured into Team Fortress 2 and Dota 2. First, we get weapons and the almighty crates, and now Valve is adding user-created content in the form of weapon "finishes." These finishes are like custom skins that you can apply to any weapon.
You can browse through and vote on various finishes in the Workshop, or even upload your own. Valve has even created a 26-page how-to guide to creating your own awesome finishes. If they get enough positive votes on the Workshop, they may even be included in a future update.
CS: GO is a fundamentally strong game, and I'm enjoying seeing the classic Valve bells and whistles being added to it.