I found this thread (http://typophile.com/node/28777) early today and was blown away by the kind of dialogue on the forum, it's very exciting.
I've got a more general question about ligatures, not just about legibility, but more about their context. Wikipedia says (I know, I know) that ligatures are "slowly coming back" because of things like OpenType fonts. This made me wonder about the use of ligatures in typography today. I'm still relatively inexperienced in the field, but have the impression that ligatures are somewhat antiquated, especially to people who might only see Times New Roman, Arial, etc in their everyday interactions with type. I'm sure they would be surprised by them.
This might be more a matter of opinion, but are ligatures (like ct, for example) more functional, or a way to express typographic tradition? I recently used Abobe Myriad Pro for the draft of a long document, and had turned on ligatures in InDesign. I was partly taken aback by the flavor it added to the text, but it also felt "older" (part of that is probably in part due to using Caslon...). I'm curious to see what my advisor's comments will be.
I couldn't find anywhere that seemed to tackle this question specifically, but feel free to direct me if there are other places to learn, etc. Otherwise, I'm looking forward to hearing thoughts.