From what I've read, the original form appears to have been "enamored of," with "by" and "with" eventually becoming acceptable.

I feel that, sadly, people will take the "easy route" and change grammar to something that sounds more familiar. (An example is the fact that many say "I feel badly," instead of the correct "I feel bad."). Grammar is just not very important to many people, but I've always loved it, so I like to use it properly.
i guess I'm saying that I feel this is one of many things that has been "dumbed down" in order to please as many people as possible. Too bad, in my opinion.