It looks like the first fan made maps for Tiberium Wars are starting to appear, there are already a selection available over on CNCDen.
Also, Lion (the webmaster of said site) mentioned a number of items related to the world builder such as people having load problems and so forth. It seems that the world builder takes up a LOT of system resources so you have to be very patient.
Here are a few tips from Community Manager Apoc which might help any budding mappers.
-Worldbuilder is not easy to use for the first time. If you have never used it before then be sure to open up the RTF manual that comes with the install. We have created a very good general introduction in to creating maps. Worldbuilder is not for the weak of heart, prepare to have patience :o)
-Worldbuilder is what WE USE TO BUILD THE GAME MAPS. That's right, as stated in the copyright, the tool you have is exactly what we used to build all the maps in the game. It takes time, it takes patience, and it takes good understanding of how to use all the power in the tool. Do not try and rush it.
-Pre-plan your maps. I cannot stress this enough. When we design maps, we don't just jump in to Worldbuilder and go for it. We draw them out, we create battle-plans, we visualize and conceptualize what we want to do before we start building. Especially if this is your first time, make sure you really think about the design when pre-planning and creating.
-"Map Balance" is key when creating a map. If you look deep in to each of our maps in Command & Conquer 3 then you'll see the rhyme and reason for every object and layout of a map. We hope to see aspiring mappers create strategic maps that have specific strategic thoughts put in to them. Those are the maps that will become the best. We challenge everyone to make the next best multiplayer map that hundreds, if not thousands of C&C multiplayer gamers will play.
Head to CNCDen for all the latest on the mapping front.