I'm not sure who among this thread's contributors has or doesn't have Lion, so just let me point out (grâce à Pogue, p 848) to artie and others who don't have Lion:
'When you install Lion, it automatically creates an invisible hidden "hard drive" (a partition of your main drive that has its own icon) called Recover HD. It's a 650-megabyte "drive" that's generally invisible to you. It's even invisible to Disk Utility, so even if you erase your hard drive, the Recovery HD is still there to help you.
That's not correct. I've verified by testing that if you erase your disk, the Recovery HD partition goes away with it.
To be precise, whenever Lion is installed on a volume, the installer automatically carves a 650MB partition out of the end of the partition you're installing onto, and puts the Recovery HD partition there. If you install Lion onto multiple partitions on the same drive, you get multiple copies of Recovery HD, one at the end of each partition on which Lion is installed.
If you then remove Lion from such a partition using a Lion-savvy utility to do so, the 650MB partition gets re-absorbed into the normal partition it follows. The obvious example is using Lion's version of Disk Utility to erase the volume, but using the Lion Installer to restore Snow Leopard from backup also re-absorbs the partition. (If you subsequently use the Lion installer to restore Lion from a TM backup, the partition is re-created.)
The only way Pogue could have erased a volume and still had Recovery HD left behind is if he used a non-Lion-savvy utility to do it. (For example, if he used Snow Leopard's version of Disk Utility to erase the volume.)
And of course you can always get back all your disk space by re-partitioning.
