I'm a big fan of the Dirk Gently-series. I don't really like how Dirk Maggs handled the end of the radio series (you know, the 'new' episodes), but I guess he didn't have a lot of choice on how to handle the situation. Dirk Gently is amazing though, I never was that big a fan of the book, but the radio series really added a lot to the world of Dirk Gently.
I wonder if the third series is ever going to happen though. Dirk Maggs won't be doing it, so unless someone else picks it up, it probably won't see the light of day. It's a shame, the third series was the one that was going to be the most interesting. A lot of rumours of a Hitchhikers-crossover (which was Douglas' own idea), of which the start was visible in the second series. A real shame. Here is my source: http://www.douglasadams.se/forum/viewtopic.php?t=14860
On the same forum (which is fairly accurate regarding Douglas Adams-info), there are some rumors of a sequel to the first Hitchhikers-movie being made as a DVD-movie, based on the radio version a bit more. There's even some concept art floating around. If this new book is a succes, I guess chances are we will start hearing more about it.
But yeah, book isn't needed. I'll skip it. New radio/television/cinema-stuff: Bring it on.