Hi, if you've already used 6 & 7, then I assume you've been through all of the built-in lessons to give you an overview of the basics, right? Plus there's a short overview there of what's new in 8. Though I took the time to read the printed 7 manual from start to finish, to be honest I learnt more by working on music - whether composition or jamming - and then looking up specific items in the PDF manual. Even better is working together with a more experienced user and asking them questions/watching how they do stuff - highly recommended.
Another nice resource are the two sticky posts at the top of the Tips & Tricks forum
Edit: another great resource: http://www.vimeo.com/user730594