This will be old news to some, but if you’ve upgraded to Lion and installed the latest version of Apple’s Developer Tools, go take a look in your Utilities folder. There you’ll find a new folder containing a preference panel called Network Link Conditioner. Just click to install it, and you’ve got a handy way to simulate various bandwidth conditions (particularly those of the paltry variety). NLC temporarily throttles your machine’s Internet connection system-wide, so it works just as well for testing the performance of your websites as it does for the proprietary iOS apps it was intended for.