Okay, let me start by saying this book pretty much repeats information throughout the book and that's simply because it's aim is to show regular expressions in Perl, C, PHP, Python, Java and .NET. So it's a little like getting a manual for your DVD player with instruction in French, English etc. when all you care about is English. However, if you happen to work in various languages (as I have in the past) then this is actually a major selling point.
I do not use regular expression often enough to have instant recall of the metacharacters etc. and so this little book (at a pretty good price) which fits perfectly into a small pocket in my laptop bag is a MUST HAVE for me for those times I do need to write reg. expression code.
I don't leave home without it :-)