When deploying Windows 7 the Network Location dialog box is sometimes shown even though the machine is joined to a domain. It’s only on specific hardware but it’s quite common.
Microsoft now has a hotfix (KB 2028749) for this bug.
A “Set Network Location” dialog box appears when you first log on to a domain-joined Windows 7-based client computer
You can set a Group Policy for Network Location – Computer Configuration / Windows Settings / Security Settings / Network List Manager Policies / All Networks. Change Network Location to User cannot change location
This is the dialog box you might get without the hotfix…