I've gotten a few people asking for some good resources for learning Dojo - so here goes. Both of these are good books that our team uses on a daily basis. Although they roughly cover the same ground, the do so in a different manner, which can be helpful when sleuthing around for solutions to some odd problem or another.
This was the first book we got on Dojo, and it's a good one. It covers all the basics (ajax requests, dom navigation etc), and more advanced stuff like creating your own widgets, which is where we really found this book useful. They get into the whole widget lifecycle, the default file/folder layout for widgets & templates etc etc. This is stuff that you'd really have to dig for on the Dojo site, so it's much easier if you have the book.
I really like all the Pragmatic Programmer books that I've read, and this one is no exception. Like all the books on Dojo, it has the basics, including a clear explanation of dojo.hitch. What sets it apart is that it has some application examples. This is nice because it lets you see how someone actually hooks a whole app together.
While I'm talking about books, if you are going to be doing any work communicating to your own services, I would also recommend RESTful Web Services - this is a great book that gives you the low down on all that HTTPGoodness you'll need to work through the weirdness you are sure to encounter.