You are all now well aware of Noah Improbablecog Beasley’s Open Source Jewelry project on Kickstarter, and you may know of Thingiverse, where Makerbot(ers) share there files to be extruded from hot gooey plastic, you may even know of Content Central, where Solidworks types (or just anyone) can upload/download 3D models of just about anything (mainly mechanical parts).
Shapeways has had the 3D Parts Database for a while, but now sharing your 3D files on Shapeways has just gotten a whole lot easier.
There is now a simple checkbox in your part page that allows others to download your 3D file.
One of the best ways to learn about 3D modeling (or any design really) is to inspect a part and see how it is constructed. By sharing your files you give others a chance to learn from your wisdom and mistakes and you get the opportunity (depending on how you chose to share) of seeing others tweak and improve your design. If you are downloading a file you get to learn from others, take small, early steps into 3D modeling by playing with an existing design, or just the thrill of seeing the relationship between a digital representation on screen which you can then have 3D printed..
If you are interested in sharing your designs you may want to include a creative commons license on your page to let others know how you are willing to share, or if you are willing to just set your babies free, tick 3D Part download, available to all.