To me the purpose of Cbeebies is to allow me the time and space to get the dinner ready. If I had the time to sit and watch it with DD, I would do something else with her instead. It just seems to melt my brain whenever I watch it for more than 1 minute.
However I know loads of people who know all the stories from a selection of different programmes (DH often comments that he's seen one of the programmes before - so he's obviously been watching a lot closer than I have!), and regularly hum the theme tunes!
I know its much more enriching for the child if you watch it with them, but I'm sure my vague knowledge of the programmes is adequate????