Windows 7 & 8 can automatically change your default printer based on which network you’re connected to.
The normal use case, of course, is to switch printers depending on whether you are at home or at work, but this feature is especially useful if you use one of the many print-to-PDF solutions—you can continue to print things even while you aren’t connected to any network.
Go to the Devices and Printers panel, and then just click on one of the printers, which will enable more buttons on the toolbar. Now you can select the “Manage default printers” button.
In here you can change the radio button to “Change my default printer when I change networks”.
And now you can select a network in the first drop-down, and then select the printer you want to assign to that network in the drop-down box.
You can also select the “No network” item in the drop-down box for anytime you aren’t connected—this is good to assign a PDF printer as default when you're offline.
Note: this does not work for Home edition of Windows 7, and only applies to laptop PCs!