cocoa-dom:

If you put in network code into your apps, it is always important to test against bad network conditions. While this isn’t too trivial, it was always possible using dummynet.

However, now new in Lion is a Preference pane to use, so you don’t have any excuses anymore for not testing: Network Link Conditioner - Use it and use it heavily - real life network conditions, especially on iOS, are never as good as in your pristine office big bad ass network location.