Where to place aux-in/USB

I recently discovered that my headunit is compatible with all the aux interfaces. I am about to install the aux-in and a DIY USB charger. I am looking for pros and cons of the different placement options, such as euro tray, cell phone mount, arm rest, glovebox, etc. Any sort of after action report would be helpful or any other creative placements.
Thanks.

I put mine in the sunglass holder. Just drilled a little hole right in the back of it and everything fits perfect. That way I can just wrap the ipod up and close the panel to it and go in a store or whatever and its completely invisible. That and it just looks perfectly OEm when not in use. It is also very easy to run the cable to it and it just pulls right out, so installation is a breeze. I have seen it mounted on the small panel that the heated seats are located on and that looks pretty good as well. Just personal preference really

I put mine in my ashtray. Figured I'm going to always have it open for access to the car charger, so I drilled into it.