I think this is the "go to" book for learning uke. The author covers the basics in a logical order and goes on to cover a wide range of playing styles. I think if you're only going to buy one ukulele book, it should be this one. I particularly like that he starts with strumming and chords, covering melodies later. Most tuition books seem to do it the other way round, which must put people off - there are only so many times I can play "Michael, row the boat ashore" without losing the will to live :)
Also, if you don't have a uke yet but are thinking of buying one, there is a good chapter on buying a uke and what pitfalls to avoid. Similar info can be found online, but it's useful to have it all in one place.