Well having found the Definitive Guide to Symfony a bit uninspiring I've spent a bit of time on the "Practical Symfony" book - online.
http://www.symfony-project.org/jobeet/1_2/Propel/en/ [1]
So far it's great - the first "three days" lessons went by pretty quick, and I'm glad I'd done some background reading.
Putting the two things together I feel I've probably got enough understanding to start writing a basic app - which is exactly what I need to do to make sense of a load of reading.
Following a step by step guide is a great way top get started - but you never really understand something till you do it for real.
Links:
[1] http://www.symfony-project.org/jobeet/1_2/Propel/en/