A superb book from Philip K. Dick. As always with Dick's novels, the sci-fi technology in the book is little more than an undertone to the rest of the novel, which develops in to an escalating identity crisis.
As mentioned by other reviewers, there are some interesting similarities to Philip K. Dick's "Do androids dream of electric sheep". For example, a few corporation names are the same. It's easy to imagine the two stories occuring at the same time or at least in the same world. For me, it's hard to tell what the author's intentions was in doing this, but perhaps one novel started out as a prelude or sequel to the other.
The plot is probably less 'deep' than tytpically expected from this author, but the story is still thought provoking and makes a thouroghly good read.