The Sporepedia is the central hub for community content related to Spore. It is there that all the user created creatures, buildings, and vehicles are uploaded and downloaded. If initial response is any indicator, the community around this game will be enormous. Millions of creatures, buildings, and vehicles have already been uploaded, and more pour in by the hour.
Sure, some of them are terrible, some are grossly inappropriate, and some are just plan wacky. But a lot of them are amazingly creative, and will either provide you will inspiration to create your own or will simply be things you begin using immediately in your own game.
You can create a buddy list and only accept content from buddies, or you can ignore all the online content completely. Your level of participation in the community is completely up to you. So far, it looks like the community will be extremely vibrant and productive - similar to the community around The Sims.