It is my understanding that the 7D has an "Integrated Speedlite Transmitter". I have downloaded and read the manual, but still not sure what the feature is or how to you it.
It means the built-in flash can wirelessly transmit ETTL info to other off camera flashes, very much like the wireless transmitter ST-E2. This video may help http://cdn.sellpoint.net/canon/EOS_7D-15_Flash.html .
Don
Another way to think of it is that previously one would have to mount the ST-E2 or another flash( eg- 580EX) on the camera to trigger any combination of remote slave flashes. Now the built in flash can do this for you.
For single flash photo's it works quite well. However for continuous high-speed flash photography it is much slower (2-3fps) than using the ST-E2 or either a 430EX or 580EX . The built-in flash will also typically quit (ie - stops firing/triggering remote flashes) after 3 continuous shots.