Is there any good source of information about the Lync SDK in gerenal, and about Lync Client Automation in general?
Free online sources are preferable, but if there are none that you know of, I'll settle for a good book (please recommend only one you've made use of).
The SDK documentation and sample apps are a great place to start.
There are the MSDN Technical Articles, a good collection of general Lync resources, and the Training Kit.
This book is really useful.
Also, keep an eye on my blog, CodeLync. It's relatively new, but i'm actively adding more content