PFDS is a very good book even if you have no particular interest in functional programming. It's not the first book you should read on algorithms (hey, they didn't title it _Introduction to Algorithms_ for nothing), but I think PFDS is a very strong candidate as any one of the first four books you read on algorithms. It's short, it's not all that hard to understand, and the data structures and algorithms there can be relevant for reasons other than purely functional programming (especially: persistence).