I started AA100 last october, so Spanghew you will be following exactly the same syllabus as I was! i started this course (and finished it!) because I wanted to do a BA in English through the OU, but for various reasons changed my mind about the OU and am now at college on an access course.
There are two intakes on this course, February and October (from memory) and this makes the course forum extremely confusing! Each intake studies every second subject on the course material, so for example Spanghew will do exactly the same subjects as I did.
There are huge vats tranches of the course that you can skip over, and still pass - I was averaging 75-80% in my TMAs - but I am anal and have no life and love studying! Some of it is extremely interesting, for me Cleopatra was dire, the history of religion in England in the 16th century I could not even read, but Pugin was fascinating.
Having now been on my access course for three months, AA100 is a dawdle! One point - ascertain from the beginning whether you are allowed to use outside sources in your research - I was marked down for it on my Pugin essay and queried it and was told it was down to individual tutors - I was raging!
The course is supposed to take, what 16 hours a week - I used to dip in and out of it and not look at it for weeks on end and still got great marks - I did my final essay on the history of the seaside which was extremely easy.
It's certainly enhanced my uni application, I have a verbal acceptance from my chosen uni, and am steaming ahead on my access course - I'm doing highers in english, history and politics and a lot of what I learnt on AA100 I can relate to my current studies, for example the industrial revolution.
OU is for some people, my mother's gained an MCs in maths and stats through the OU last year, personally it didn't work for me, I prefer the face to face interaction of lectures and group work, and it's entirely hit or miss on the tutors - I've done a number of 10 point short OU courses and my tutor on AA100 was barking - seriously, I met up with her and was even more confused by the end of the meeting!
Good luck, anything else you want to know just ask.