My 2 year old suddenly took against bath time, but with a little blackmail and corruption and bath crayons we've just had a lovely half hour. She was totally engaged and engrossed, loved drawing on the bath, and cleaning it off after. So no worries in my house about having to scrub the bath afterwards. I did notice that they wiped away much easier after the first time, so maybe ensuring the surface is wet before you start drawing could solve the issues people have had with cleaning. We just used an old sponge - they do a set for an extra few pounds that comes with a sponge, which seems an expensive way to do it.
I stole another reviewers idea of floating them in a tupperware type pot - inspired!!
8.00pm and I have a sleeping daughter upstairs, clean, happy and no upsets. Heaven!
Now I just need to find a product that makes hair washes just as attractive.