I read the thread that Steph linked to and, like you, thought it would be great so did lots of googling and nearly spent £20 on one. BUT, I'm glad I hesitated. Before I bought I decided to try out the principle first and borrowed this from my 6yo DS for about a week:
(((DON'T LAUGH!!!!!! (Well, you will, but never mind))))
http://www.farmtoysonline.co.u....._Blue/534/
The bag bit is almost exactly the size of the organisers that they sell and very similar in design to some of them too.
What I found was that it was a pain putting everything back into it every time I took out eg my cell, keys etc and I wondered if actually I needed the opposite: a small bag that I would fill with everything that *shouldn't* actually live in my handbag that could be removed at the end of the day. Needless to say I never followed that up, but perhaps I will.
My point is that for me I had to try out if the idea would work for me first (it didn't) - then if it had worked I would have investigated more. It certainly saved my some money and I may try it again in the future.
PS I didn't put the trowels/forks etc into my handbag...