The most basic problem with ligatures is that they were a technological solution which is no longer needed. Yet typofiles are often such traditionalists that they're afraid to let go of them. The English language is complicated enough with exceptions for this or that. Connected letters are not a standard part of English. Foreign readers are used to special characters meaning special things or having special pronunciations.
Ligatures do neither, they're just for looks.
As more and more type is read on-screen, ligatures should be avoided entirely. Monotype's FontMixer does one thing, but it does it well-it lets you rearrange and mix the characters from Type 1 fonts. The only way to access them, however, is by using Monotype's FontMixer program. It takes less than 30 seconds to add them to your character set. Select the ligature, select the character position where you want it to appear, and replace the existing character with the ligature.