If you're considering buying this book, chances are that you know about the web site. If you haven't seen it then search for it now using the obvious key words from the book's title. If you find it funny then you'll probably find the book funny. If you don't like the web site then you won't like the book.
It is basically as simple as that, except that I thought the web site is excellent, but it doesn't quite translate to the book somehow. I did think it was a worthwhile read, but it's just not the same. However, what I did think was brilliant is the weird little footnotes that appear on almost every page and give insights into 'Robert Hamburger'. The wording used and the style of writing is presumably all part of the character, and really pretty well done.
That said, if you just like stupid stuff about ninjas wailing on guitars then that's all top quality too.