Great - thanks for all the replies to the thread, guys. It's nice to get so many opinions on the subject.
At this moment in time, I think I'll go with an average of two/three advancements per session, and give them out after each session. Maybe 'my lot' are an impatient bunch, but I really don't think they'd be happy with having to wait 3 or 4 weeks/sessions (about the average length of one of my adventures) before seeing their characters improve.
One thing that really attracted me to the new addition is the idea of fleshing out the characters' lives outside of adventuring. How many D&D characters have effectively been highly skilled hobos, wandering from one place to another without any roots? The idea of research and training offering benefits to characters might counter that. 'Real' people wouldn't want to abandon their lives to adventure constantly and I felt these rules might reflect that. As well as the satisfaction of completing a scenario, characters would look forward to pursuing their own interests and concerns. That seems so much more believable to me. And, yes, I know you can encourage this with D&D (and I have had the occasional player forge a few magical items or pay lip service to a relationship), but it has rarely seemed an important part of a character's life. For me, research and practice should offer some tangible reward to characters - though not as much as adventuring or they'd never want to do any (I had a very brief Ars Magica campaign where the characters refused to leave their castle: they were too busy training!). :lol: