California Growers Exemptions...

... so whats the deal with these? They seem much harder to find info on than standard patient cards (which makes sense). I was of the understanding that if you get one, you're allowed 99 plants (with some limitations on the area of the grow area and/or canopy).

Is there a list of places you can go to obtain one? What does one need to do to qualify for one? What else should one know?

Thanks!