I've been exclusively using Macs since 2008, and have been very happy with the change in ecosystem. But recently, as my proficiency with the basics of OSX has reached a sufficient level, I have realised that I remain woefully ignorant of its inner workings, and I'm sure there is so much more I could be doing/utilising. So, could you recommend a 'guide' to becoming a knowledgeable user of OSX? I don't mind paying for it (within reason), but free is better. (I've used Leopard, Snow Leopard, and am now on Lion).