Where do I begin?

Well, until Matt Sullivan & Sarah O'Keefe's new FM11 unstructured book comes out next year, I would highly recommend the Scriptorium FM8 Unstructured reference text - it's like $10 for the PDF version. Sure the UI looks different from FM9+, but the operations are pretty much the same. The Adobe Tech Comm blog has lot's of material for getting you up to speed with the newer version features.

Welcome back to the FM world! Were you using stuctured or unstructured FrameMaker? The structured side has evolved the most. It may look like a lot has changed, but that's primarily the interface layout. Otherwise, the skills you had back then still work the same way now (especially if you used the keyboarrd shortcus).

To get up to speed on the OWL interface, there's an Adobe online video at: http://tv.adobe.com/watch/tips-and-tricks-for-technical-communicators-to-maximize-productivity/getting-started-with-the-new-framemaker-9-user-interface/

The other really significant feature is the introduction of unicode support with FM8.

To get a good idea of what new features have been added to FM, I'd recommend reading through the Reviewers guides for the various releases to see how FM has evolved:

FM5.5: http://www.adobe.com/uk/aboutadobe/pressroom/pressmaterials/pdfs/framemaker55/FMrg.pdf

FM6: http://www.adobe.com/aboutadobe/pressroom/pressmaterials/pdfs/framemaker/fm6newfeature.pdf

FM7.2: http://www.adobe.com/aboutadobe/pressroom/pressmaterials/pdfs/FM_7_2%20Reviewers%20Guide.pdf

FM8: http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/devnet/framemaker/pdfs/fm8_reviewers_guide.pdf

FM9: https://share.acrobat.com/adc/document.do?docid=75864237-da11-4fbf-bbcc-90cda2bed045

FM10: http://www.adobe.com/content/dam/Adobe/en/products/framemakerserver/pdf/fm10_fms10_complete_reviewers_guide.pdf

FM11: http://wwwimages.adobe.com/www.adobe.com/content/dam/Adobe/en/products/framemaker/pdf/FRAMEMAKER11_REVIEWERS_GUIDE.PDF

[Note to Adobe: It sure would be a heck of lot easier to find, if you systematically filed all of your material in the same manner and same reelative locations]

The best (currrently available) resource is Scriptorium's Unstructured FrameMaker 8 book (see: http://www.scriptorium.com/books/publishing-fundamentals-unstructured-framemaker-8/). However, the book is being revised for FM11 by Matt Sullivan and is due out really soon. See: http://framemaker.mattrsullivan.com/2012/07/25/framemaker-11-book-project/

I hope this helps you get started (again).