Does "apropos" take a preposition? How do you use this word, anyway?

Which is more correct:

Apropos of your earlier comment, I decided to....

or

Apropos your earlier comment, I decided to...

Actually, apropos is so fancy a word, even I, a word maven if I do say so myself, am not entirely sure when to use it. If I may add to my preposition question, are there any constructions where it would be appropriate to use something like with regard to and not apropos?

Answer

The answer to your either-or question is "yes". :)

In other words, apropos can be an adverb, adjective, or preposition on its own, or it can be used as part of the prepositional phrase apropos of.

Depending on how you want to use apropos, synonyms can include "by the way", "incidentally", "regarding", "concerning", "opportunely", or "appropriately".