I gave myself an hour. There had to be a time limit or I'd have been there all day - but it was such a fun hour! Once you've got over the initial 'hmmm, what to draw, don't want to ruin it' thoughts - and just doodle, doodle, doodle.... it's fun. Therapy, I think.
Here's the results - odd that my doodles turned into a kind of bonkers town, complete with resident mermaid and one lone cow. Must say something about my inner self.... ;-)
For all those in need of some doodle therapy, (and I would recommend it to many of my friends!) get yourself a tshirt from here and start doodling!