Just a tit bit of information for our users out there.
The variable that stores the location of the Android SDK that unity uses can be found here for mac users:
Macintosh HD > Users > [user name] > Library > Preferences > com.unity3d.UnityEditor3.x.plist and looks like this
For windows:
HKEY_CURRENT_USER\Software\Unity Technologies\Unity Editor 3.x and looks like this
Name: AndroidSdkRoot Type: REG_SZ Data:
I’m only posting this as one user was not getting the pop up box to be able to point unity at the location and this was a surgical approach to setting the variable.
Not really sure this is much use to anyone but at least the information is out there.