Hi,
Yes I do turn off my box, TV and router at the mains every night before I go to bed and have had no showcase or on demand when I turn them all back on in the mornings.
HOWEVER...after reading that someone pulled the plug out completely and then plugged back in and re-booted and it worked, I thought I would do the same just to see if it worked and OMG ! yes it did :O)
I just unplugged my box and TV for about 30 seconds, then re-booted and the Showcase and On Demand is back on and working.
Maybe switching it off using the plug switch is not enough and there is some residual current going into the box which is keeping some error info on a memory chip or something ?