Copying OSX to SD card from rMBP 15"?

[Mutters]

Has anyone done this?
Putting a copy of the OS on an SD card seems like a good idea, seeing I'm on a 15" Retina MBP.
It's also for the fun factor - how long does a boot take from the SD slot, type of thing.
I've been through the guide for booting from the internet, an amazing ability in itself, but haven't actually tried it.
It's not clear - to me at least - whether one can download OSX without having to pay for it again.
Thinking on it, one would imagine not, but, who knows?
Or, can it be copied directly from the boot partition?

So, yeah, anyone done this, or know how it's done?

Ta

[leon]

I tried it on my 2010 Mac Mini server. It was slow as buggery (took around 10 minutes or so to reach the login prompt) and would only recommend doing it in a tight squeeze where you need to try and access data off a machine that won't boot.

It could have been due to the speed of the card I was using (not a very fast one at that) - standard Sandisk from memory.

[mmulhern]

I installed express card34 SDHC adapter in my MBP'08 and installed OSX to it. I use that as test partition for playing with software and settings.

I've even installed 10.7 on a 32GB microSD card (class10) for my MacBook4,1 that sits in a USB mini adapter, only small bump about 3mm sticks out of the USB socket. Boots fairly fast, don't recall actually how fast, but it didn't seem deadly slow.

Lots of fun, but not the fastest. Really should get a GeekBench value on them both this weekend, and time to desktop.