Almost Canon will release a new firmware update for the EOS 7D in august. http://www.canonrumors.com/2012/06/canon-eos-7d-firmware-version-2-coming-soon/
does that mean you can hold down the shutter and shoot for as long as you want or just in a pre-defined burst?
It means that you can shoot a burst until it hits that many shots. So right now if you hold down the shutter you'll hit the buffer at 15 shots, meaning you can't shoot anymore until they process into the camera. After the update you will be able to get 25 shots until you hit the buffer.