Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:381529.
** Update: New fan version up at http://www.thingiverse.com/thing:382809**
So, this model had me really excited. It printed out well, it was my first time designing a fan (had my doubts if it would move air well), seems to move air great when hooked up to the hobby motor I have, and it was done entirely in Sketchup (I'm sure it would have been easier in other programs.
The fan is reversible, there is good air movement in either direction you run it. You'll probably want to be somewhat careful when pulling this off the print bed, the blades are fairly thin. Personally, I made sure all the blades had broken free of the bed and then just grabbed the center piece with a pair of needle nose pliers to pop it the rest of the way off.
This fan is part of a design I'm working on to make an airflow system in 3 inch PVC piping. The fan should (untested, the blades flex out a bit during operation when printed in ABS) fit well inside 3 inch PVC piping. This might get modified depending on how the flexing of the blades affects fit. After the blades are successfully tested, I'll also be uploading connectors and housing for the 3" PVC pipe.
** Obligatory Warning **
Rotating something at high speed can be dangerous, always be sure to take proper safety precautions such as eye protection, etc to protect against possible failures.