Percona is a drop-in replacement for MySQL server, it comes with built-in improved performance that will make your server fly a bit faster (or perhaps a lot!).

Before using the repository, you should add the key to apt

$ gpg --keyserver  hkp:// --recv-keys 1C4CBDCDCD2EFD2A
... [some output removed] ...
gpg:               imported: 1

$ gpg -a --export CD2EFD2A | sudo apt-key add -

Add Percona repository

deb squeeze main
deb-src squeeze main

Remember to update the local cache

$ apt-get update

After that you can install the server and client packages

# apt-get install percona-server-server-5.5 percona-server-client-5.5

Enjoy :)