Ran into a situation today where I had to roll back the UI of our test environment to pre-Sharepoint 2010 visual styles.

A simple command does the trick:

1. Open SharePoint 2010 Management Shell
2. Type in the following command:
3. Get-SPSite http://[site] | get-spweb $_ -limit all | Foreach {$_.UIVersionConfigurationEnabled=1;$_.UIVersion=3;$_.Update();}

This command will look at the Site Collection that you specify and roll back the UI version of every subsite to UIVersion 3 which is the pre-SharePoint 2010 user interface.