When implementing eRCP for the S60 platform, we use three main resources in our SWT/eSWT implementation team at Nokia. SWT/eSWT javadocs. SWT book by Steve Northover & Mike Wilson, also referred as "the book" within Nokia's eSWT/eRCP team. And the most important, the source code for the existing implementations.
I have been chatting with a fellow eSWT implementer for an up and coming implementation a while ago. He complained that "the book" is no longer available from Amazon. It looks like amazon no longer has it, so does the publisher's site. But no need to panic, I found out that safari books online includes it. If you prefer paper & ink books over online, like myself. Unfortunately, I have no information on the future availability.