How to Uninstall Windows 8, Windows 7 or Any Other Version Of Windows

If you created a second partition and installed it to the second partition while leaving your original installation of Windows 7/XP/etc on the primary drive, then yes you CAN uninstall it while retaining your old boot sector. The steps are easy:

1. Boot into Windows 7
2. Access the MSCONFIG program by going to 'Start', 'Run', 'msconfig'
3. Go to the 'Boot' tab and remove the Windows 8 boot option by highlighting it and clicking 'Delete'.
4. Highlight your Windows 7 boot option and click 'Set As Default'
5. Close out MSCONFIG but DO NOT RESTART.
6. Access your Disk Manager snap-in by going to: Start Control Panel Administrative Tools Computer Management Double-click 'Disk Management' in the left pane
7. Find the VFD you created for the Windows 8 installation
8. Right-click on it
9. Select 'Delete Volume' (BE SURE THIS IS THE WINDOWS 8 PARTITION AND NOT ORIG OS!!!!)
10. Right-click on the now empty volume and select 'Shrink Volume' (This will merge it back to your Primary)
11. Ensure your C: Drive is marked with "Boot, Page File, Crash Dump, Primary Partition"
12. Close the Module
13. Reboot the System

If you DIDN'T install Windows 8 to a new partition and Dual-Boot your system, you will need to use the Backup Disks. Your Recovery partition (F2, Alt+R, etc, etc) may not be available if you've deleted it during the install so always have a backup or full disk IMG on hand to recover.
No, you can't simply uninstall this preview. Had you read the FAQs:

Can I uninstall Windows 8 Consumer Preview?
No. To go back to your previous version of Windows, you'll need to reinstall it from the recovery or installation media that came with your PC. (Unless you installed it to a separate partition, in that event READ ABOVE!!!)

"Is there a workaround?" you ask with a twinkle of hope in your voice. No, it appears there is not. If you have the recovery discs or an image of your system, you might be in luck. If you boot from Windows 7 you will notice that the windows 8 preview cannot be downgraded to Windows 7. (YES IT CAN) You would need to do a clean install.(NOT IN ALL INSTANCES) Maybe you search for a restore point, but you didn't make one..
"Oh but I hate it, I have a list of complaints, maybe I'm irrational as well. What can I do?" You can read about something before you do it next time I've already linked the FAQs, but:

Are there risks to installing Windows 8 Consumer Preview?
Yes. Windows 8 Consumer Preview is stable and has been thoroughly tested, but it’s not the finished product. Your PC could crash and you could lose important files. You should back up your data and you shouldn't test Windows 8 Consumer Preview on your primary home or business PC. You might also encounter problems like:

 - Software that doesn’t install or work correctly, including antivirus or 
   security programs.

 - Printers, video cards, or other hardware that doesn’t work.

 - Difficulty accessing corporate or home networks.

 - Files that might become corrupted.

You should carefully balance the risks and rewards of trying out the Windows 8 Consumer Preview before you install it.

You did backup your data, didn't you? You should always have your data backed up. Then this wouldn't be a problem. Maybe you could try backing up your data from the Windows 8 preview and doing a clean install? Ultimately, there is no way to rollback the windows 8 consumer preview without doing a complete restore from a system image or recovery partition/discs