I had to keep one for the 7-8 years it took to become a Chartered Engineer. I don't know if it still is, but it used to be an Engineering Council Requirement.
I haven't subsequently kept it up, and the fact that it's not in a specific format meant that I ended up with about 200 pages of it (which are still on the shelf) which is arguably a little over the top (mind you I have always been a busy chap).
It worked for me, and certainly bears consideration - although I don't think it can ever totally replace a CV.
G