Lately I've been reading a lot, but it's mainly tech-oriented:
David Pogue's Mac OS X: The Missing Manual: OS X is great, but there's a lot of very useful stuff in this book that I wouldn't have otherwise known. There's also a lot of stuff that's obvious to me, but wouldn't necessarily be to people who haven't been using the Mac OS for years. Highly recommended if you're taking the plunge, or have already.
I'm also reading Apple Computer's Object-Oriented Programming and the Objective-C Language PDF book (downloadable with the latest development tools from the Apple Developer Connection): While I'm not an Objective-C programmer myself, I'm interested just in the learning process here, and seeing what I can pick up. I've been using this to fill in gaps in my knowledge as I work through Aaron Hillegass's eminently readable Cocoa Programming for Mac OS X (more info at his Big Nerd Ranch site). Very approachable book, but even he recommends the Obj-C PDF.
Where will this all lead? I dunno, but the Developer Tools CD came with the OS, so why not check it out? (And for the bandwidth-enhanced, the December 2001 flavor of the Developer Tools contains the supposed-to-be-awesome Applescript Studio. Free Apple Developer Connection membership required for the free download; the bandwidth-impoverished may order a CD for $20.)