Using quick parts in Office 2007
This post is from 2008 and kept as an archive. What it describes may have changed since.
A nice feature of office 2007 is the quick parts functionality. I use this in Outlook to insert often used texts into my e-mails.
The only problem is to remove entries off the list. I found an easy article describing a way to do this with Word 2007.
You can find it here: http://www.watchingthenet.com/save-and-reuse-frequently-typed-text-in-outlook-2007-with-quick-parts.html
If you only want to change a quick part, you can just save the changed text using the same name. Outlook will replace the previous one.