Just bought one of those for my 2GS, and wondering whats a good location to put it. It is a pretty big unit afterall.

 

mine fit pretty snug under the dash, like near the ashtray but towards the left of it. It's in my 3gs though. It was a good spot so the wires to the headunit didnt need to run very far and the output to the ipod doesnt need to run very far.also it's in a spot where it really cant follow or move