At the moment we're planning a trip for April/May 2011 and I've got quite a collection of guidebooks. Like Carol, I buy both and love reading them of an evening when I want to relax and use the internet and forums such as these to get more information, updates and accommodation reviews.
It's difficult and expensive to get RS books in Australia so I order them all through Amazon, even with shipping it's still much cheaper. Lonely planet Guides here are about $40 and although they're in depth, I have noticed alot of references to events, etc that happened a couple of years ago.