Do You Use Ligatures Regularly?

In a recent Publish article by Andrew Pfeiffer on Mac vs. Windows there was one passage that jumped out at me. Pfeiffer stated,

"The standard Windows character set does not support ligatures (specially designed glyphs which replace the letters "fi" and "fl" in many fonts). Ligatures are barely known to casual users, but they are a big deal for type-conscious design professionals. "

Are they, really? I can't find it now but I recall a forum discussion from a while back where we were discussing the use of ligatures. While most everyone knew what ligatures are few used them on a regular basis. Do you? What is your criteria for using ligatures - all the time? only for very formal documents? only on headlines? only when the client is paying extra for such attention to detail? only when you think about it? Tell me about your use (or non-use) of ligatures in your design and publishing projects.

Definitions: Ligature | Diphthong