Thanks decrepit Joe (815 AD or BC?) :)
I'm not worried about people being able to see the filenames, just about whether knowing the file structure (via the .xxx extension) would make brute-force attacks viable. From reading around, and from your reply, I don't believe that it does.
I have read about people having problems with the pathname lengths, and several comments that led me to believe that the encrypted filename changed with each save (but I admit that this might be a bad inference on my part).
Anyway, thanks for the reply - for now I'm sticking with unencrypted but I will probably experiment with encrypting (just to see what happens to pathname lengths and filenames for myself).
BTW - Go look up who invented the "flyball governor" and when.