I've had a waiting list for this book since last April (2009):
It wasn't due out till April 2010, but it arrived at our excellent local independent bookshop early, and they phoned me to let me know (see what I mean by excellent?). There are several very happy borrowers as a result.
Skulduggery Pleasant book 5 will be out in September 2010 - yes, this is a double Skulduggery year - and Skulduggery Pleasant book 6 a year later, in September 2011 (according to the information at the back of this one).
PS. I now have a waiting list for Skulduggery Pleasant book 5. Of course!
PPS. IMDB still shows the Skulduggery Pleasant film as having a 2010 release, but as it's in development, early days by the look of it, I'd not be holding my breath.