Sorry to bring up an old thread, but I'm going to be doing this soon. Thanks for the instructions, Tom, but there's one problem with them: they explain how to boot to an external device with a fresh install of OSX. It doesn't say anything about migrating the existing OS to an external device. How is that done? It must be possible. I recall that I migrated to an SSD on my own MacBook years ago, but that was for a drive swap. Not an external device. I assume that the instructions above would still apply, but that part in the middle where they redirect to another page of instructions for installing OSX from a recovery partition would instead involve copying the system over to the new drive...

Thanks for the help.