How to downgrade from Mountain Lion back to snow leopard with Time Machine

Question

The final straw was the horrible mouse sideways page wiggle while trying to scroll down and read safari pages. Even after turning the feature off, tech support said it will still wiggle a little. That and the HORRIBLE grey icons everywhere was enough to send me back to my beloved iMac I loved when I bought it. I'll give up the iMessage and the few new items ML gave me. But as many others said, what I got new was far less than what was taken away. 
So what tech support had me do was this. Even though the apple engineers said it would not work, apple tech support had me try it and it worked for me so good luck. Engineers said that after you install mountain Lion, it messes with ALL your time machine back ups and won't revert back to snow leopard even if you select a snow leopard date back in time.  That didn't happen to me.  I have a 2010 27 inch iMac
This worked for me but PROCEED AT YOU OWN RISK
Export individually any email folders or photos or data you will lose between now and the date you are reverting back to.
1. Insert Snow Leopard DVD that came with computer. The install disk not the applications. Make sure time machine external drive IS connected.
2. Restart computer and when you hear The Mac chime, hold down the C key and then it will take several minutes to boot up from the DVD.
3. Select the little blue triangle to continue in English.
4. When it gets to the screen that says "continue" stop. There might be a screen or two before this one I can't remember but either way stop at the word continue.
5. Go up to the top left and find the UTILITIES pull down menu and select disk utility.
6. In the window that opens up, Select the Apple drive which should be the very top one in the window.
7. Select erase.. it should be Mac OS extended journaled
8 select erase and maybe a password. It only takes a few seconds
9 go back up to UTILITIES in upper left and then select restore from time machine or backup or whatever it says. It's the last choice.
10. Select the external time machine drive and navigate to the date you last had Snow Leopard running and that will be the date it restores to. You will lose any data between now and then but you can export your mail, export photos, and other items separately. I only stayed on ML For a few days before hating it enough to go back so I had no loss of data except a few emails.
11. Hit RESTORE. And then it will take several hours. When you restart it, it should come right back to that day you selected as if ML  was just a bad thought on someone's drawing board.   If for some reason it still comes up ML, Then they said to erase HD Again (steps 1-8) and then manually drags back USER folder or individual folders with Mail, photos etc.   if this way doesn't work, have another plan printed out so that you are not stuck by this one.
Good luck. Proceed at your own risk..

Answer 1

The ultimate solution:
You need an USB of at least 5 GB and the Snow Leopard Install DVD.
1. make a bootable USB with Disk Utility in it:
     a. download the Mountain Lion Installer from the App Store
     b. quit the installer after download
     c. find the installer in the Applications folder
     d. option+click in it and select "Show Pakage Contents"
     e. go to Contents>SharedSupport to find there the InstallESD.dmg file and mount it by double-clicking it
     f. with the Disk Utility, restore its contents into your USB
2. boot from the USB:
     a. restart the computer and hold-down the option key while booting
     b. select the USB and boot
3. run the Disk Utility and format in ONE partition the HD of your computer
REMEMBER: BACKUP YOUR HARD DISK BEFORE DOING ALL THESE, YOUR DISK WILL BE EREASED AND DATA BECOME UNRECOVERABLE OTHERWISE
4. insert the Snow Leopard DVD and reboot from it
5. follow the on-screen instructions to install OS X 10.6
After this, you can, if you will, upgrade to Lion or stay in Snow... Good Luck!!