From Scott Watermasysk:

Keywords are a list of words/symbols/patterns that when found in the body of a post or article will be replace with a link and text of your choice. To add keywords, you must login to your blog and select the Options tab >> Keywords.

Some of the features/configurations of keywords:

• Case sensitive
• Replace first instance only
• Open link in new window
• Ability to set a tooltip/href title

There is one caveat to mention. All current versions of .Text are hardcoded to only use Keywords the first time a post is saved (whether it is mark as published or not). I was afraid of adding a feature that could not be turned off. With the new configuration storage options, .Text will be getting much more flexible you should be able to explicitly configure this option.

So, you really need to decide ahead of time what links you want to have globalized, and do it before you submit all your blogs.