Steps involved in Uninstalling SQL Server service packs

Hi,

Came to know that we can uninstall sql server service packs from SQL 2008 SP1 onwards.

Question is, for suppose i have installed SQL 2008 SP3 and found problem. Now I want to uninstall SP3, what are the steps involved to uninstall a service pack? Can we also uninstall QFE, Cummulative updates and hotfix's as well?
How does sql server does the rollback or uninstall of service pack behind the scenes?

Appreciate your help.

Thank you.