If you are like me, you were eager to try Lion and installed it over Snow Leopard, and didn't clone your SL install before installing Lion. And if you are like me, you hated Lion. Hopefully like me, you had Time Machine backing up your SL install all along. After a bunch of research, I found very little concrete accurate advice as to how to revert to SL. But buried on a random web page somewhere was the exact info I needed. So here it is... Remember to back up any files or folders you created after installing Lion, as these will be gone when you restore. Also remember that this will only work if you included system files in your Time Machine backups. It's quite simple really. You boot into the Lion Restore partition (restart, hold Option, choose the Lion Restore partition to boot into). Choose restore. Scroll to the latest Snow Leopard date and select it. Hit next. Be prepared to wait several hours (I did it overnight). When you're done, you will be back where you started before installing Lyin. A little side effect from Lion remains...the restore partition. Again, a bunch of research on how to get rid of it proved inaccurate. You may be able to boot into it for Time Machine maintenance...I don't know, I didn't try. I just wanted the 650Mb back. After restoring, I rebooted and the Lion Restore partition was no longer hidden. It appeared on my desktop. It was then a simple matter of using disk utility to delete the partition, automatically merging the free space back to my SL install. The only glitch I've encountered so far was that moving files to the trash resulted in a warning that they would be removed immediately. This was fixed with a terminal command which deletes the trash folder and rebuilds it. A restart and I was back in business. Sorry, I don't have the code handy. I hate not having the latest and greatest offering from Apple, but in the case of Lyin, it may be the latest but... I don't see reverting to SL as a downgrade at all.