Hey guys, I recently researched this one to hell and back and I ended up getting my MMIC (medical marijuana info card). I only learned what works in San Diego -- check your county website for your specific procedures. You still need a doc's recommendation (MMEC is where I got mine), and then you go to the county office and pay ANOTHER 170 bucks and have an 'interview' with a county records clerk. They basically tell you that it's still federally illegal, that Cali tried to enforce the plant/bud limits but that's been found unconstitutional so you can pretty much have what you want. But don't sell, and wink-wink 99 plants or less would be less likely to land you in DEA sights. Within a month they send you (or you go pick up) a card that has your picture and a number on it. If you have this card, and are within state law, no state and local cop can arrest you (assuming you're not doing anything else against the law -- good luck with THAT). They call in the number and get a VALID or INVALID status. The card isn't even linked to your name -- your name's not on it.
Then you have to renew the doc's recommendation AND the MMIC every year -- follow the money, people -- so for me it's looking like about 300 bucks a year between the MMEC docs recommend and the county MMIC card. But a cop can always drag you in and make you prove your recommendation is valid even if it's embossed. If that MMIC comes back solid, he can't do shit -- legally at least.
Hope it helps.