I'm not some typical over-zealous zombie fanatic of anything, but I'm a big enough fan to have definitely thought about it.
There are technically ways in which something similar to a zombie-outbreak can start, but nothing along the lines of being dead and raising from the grave. I think I read an article awhile back that said there was some rare bug whose bite did something in which the writer said could actually cause the start of some apocalyptic scenario were people bitten insistently without stop. I don't remember what it was, though... It might have simply been a bite that rendered you to that mindless, animalistic state....
I honestly don't remember, but there are biological related scenarios that actually could cause an apocalypse. However, these specific scenarios are said to be so extremely unlikely that I cannot see it happening in my own lifetime. So, despite having thought and planned about it in my own head, I have not personally begun stocking up on any form of rations. When the time comes, I will fight to keep me, family, and friends alive. I've got a machete, a schimitar, a dagger, a steel bat, and the willpower to break into a gun store and grab a few shotguns and ammo if necessary.
I have not physically prepared for it. And I hope I never have to.
That's the thing with situations like this. People want this to happen, out of the simple survival fantasy. Hell, sometimes I think that I want it to happen, too! But the truth is, we all know that once that starts, you're gonna' wish you never had wanted it in the first place and you'll just regret saying so.
Unless you're like Darryl from The Walking Dead - don't give a flying ********]