Seth takes a whole book to tell you what you probably already know about "idea viruses" and the bits you didn't he could have told you in a few pages. It's not truely devoid of merit, it's just like many books of this sort, it doesn't tell you how to do something, which to be fair Godin says this much himself towards the end of the book, but it does give you those sparks... "Ah we could do something like that" or "We do have advocates who might be able to help".
The Idea Virus is guilty of rebranding other marketing ideas with cheesy new names, calling Advocates or Opinion Formers, Sneezers etc, but it is an easy to read book that does give some insight into why good ideas have worked.
It is not a book that for a few pounds investment will make you millions! - But it probably made him loads!
If you are studying business/marketing etc, then this book is great for providing "real world" examples.
A book of his that I'd really recommend is the Big Red Fez - which tells you how to make effective, marketing driven websites and it does tell you what to do.