This is a very handy book to have around. It contains 100 tips covering all sorts of sysadmin type tasks. Particularly useful in my opinion, was the section on SSH, and the one on Backups.
The book has a very good approach. It starts off by introducing the hacker mentality (that's the good sense of the word too, nothing to do with those nasty crackers), and each section has a bit of background on exactly who will find it useful, and what it covers.
All hacks presented take security into account, which is an important consideration these days, and all are very well explained.
It's not all roses however.
The book suffers from numerous typos, some in the "hacks" themselves. It reads as though it wasn't very well proofed and possibly rushed out. It is a first edition though, so hopefully these will be fixed. Also, like all O'Reilly books, it has an online site with an errata section. Now, I'd far rather they got it right first time, as the whole point in buying a book is not to have to use the web, but since we can't all be perfect, it's a good effort! :)
My major problem with this book is value. There will be a few things in this book of interest to sysadmins, but most seasoned Linux types will know how to do most of this stuff anyway. It's hard to justify $110 for, say, 5 good tips that once you've learned, you never refer to again.
All in all, a great book that suffers a little from bang-for-the-buck issues.