Well - it's Jon Chappell and Digital Rebellion you should thank !
I pretty much fell in love with FCP from the first day I laid my hands on it. After 7 or 8 years working on Avids, I found something about FCP which was just intuitively right for me. But the one thing that really bugged me was that scratch disks were set at the program level rather than per project. Like you, I often have multiple projects on the go at the same time, with the media for each residing on seperate external drives. While Preference Manager is mostly seen as a neat way to trash preferences, to me it's real strength is the way it solves this problem.
Hope it's working for you... ?
Mike