I want to say that I have read and bought many versions of this Handbook over the years. The Second edition was absolutely critical for my first out of college job as I was having to run every UNIX system they covered and some that they didn't. When I am training new system administrators I make sure they have a copy and make sure they take the time to read it. Those that do, I have found make good system administrators even if they end up in Windows land because the basic skills taught in it are useful everywhere.
The Linux System Administration Handbook was very useful to me because my background was Red Hat, and every Debian system I have not completely trashed has been because they had the right pointers and translations to make me somewhat competent there :).