UPDATES *
6/4/14 - I have added a version 3 STL file that increases the room for the fan, and also removes built-in support since that has been difficult to get out. The new Slic3r supposedly has much better support generation. This is untested - if you print it, please comment on your results.
Original v2 STL - while the 2 breakout sections are somewhat difficult to remove, the CAD view does show the yellow breakout sections - just do it slowly and carefully. This cooling fan has been in continuous use for 2 months now printing cameras from my Kickstarter Pinhole Printed project (http://www.pinholeprinted.com). It works very well and as yet, I have not seen a need to improve on it by using a second fan.
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This is a cooling fan for my E3D, mounted in a Solidoodle 3. The original hot end plugged up once too often and so I installed my E3D, which works really well. However, the E3D has its own fan and the size makes mounting a separate print cooling fan difficult. So I combined the two into one 40mm fan, which runs continuously. Two-thirds of the airflow goes to the E3D heatsink and one-third is diverted to cool the print. There's no control over the airflow to the print. It's not perfect but it works pretty well and doesn't reduce the build volume of the Solidoodle 3 anymore than the E3D did. The cooling circle is partial to allow for the E3D heater and thermistor wires.

How I'd put it - if you're not having a problem with hot filament, you don't need this. If you want to cool your filament some, then try this. Be sure to check the instructions, now that it's under another tab.