What MeStinkBad is saying isn't anything to do with Program Files or system vs. user data.
His point is that mIRC currently stores everything inside AppData - a hidden folder, which isn't appropriate for some of the things it stores. He's suggesting that things such as downloads should default to being stored within a non-hidden subdirectory of the user's folder so that they're easily accessible from outside of mIRC (eg. Explorer).
Which is probably a valid point, at least for downloads and sounds. There was
another thread about this on the Feature Suggestions board.
