Thought I kick in and post a little something for those who are still thinking on buying this.
This is my first regular expressions book and I absolutely don't regret buying it. The examples are well explained and covers a lot basic stuff for starters (like me, although I have fiddled with regex before but right now I learned so much in the first chapter that it's just amazing what it can do). I also think having buying the book is pretty much an advantage, for example minor issues like the internet going down for hours could hold your progress pretty much a lot.
I don't believe I'm going to be doing a lot of regular expressions (at the moment), yet I feel it adds up to my current skills and it will possibly have a better use in other areas (or other programming languages).
Oh yea, another thing is that the third version covers PHP more. I read in the introduction that second edition and first didn't had anything about PHP, so please be sure you buy the right one (THIRD EDITION).
Cheers!