I haven't read the whole of Chris Smith's book yet, but so far I can recommend it, it is well written, nicely formatted and generally easy to read. I have two other great F# books as well, but my impression is that Chris Smith's book is the best introduction to F# I've seen yet.
Don & C9, thanks for another great video!
BTW: I simply cannot resist the temptation to point out that one of the code examples can be simplified, in the allFiles function, the following is used:
for file in Directory.GetFiles dir do yield file
which is equivalent to:
yield! Directory.GetFiles dir