Can I boot from a "bootable clone" on different Mac models? As part of my backup process I create a bootable clone of the HDD of my iMac. I have booted my iMac from the backup to test it works, this would be fine in the case of the original drive in my iMac failing.

However, would I be able to boot a MacBook from this backup?
The short answer is "yes".

So long as the Mac model was supported for that version of Mac OS X then you can boot it off a system built on any other Mac. This means that extremely old machines may not work with a recent OS X and brand new machines won't work with older versions of OS X but generally you will be OK.