Yes, its a good idea in principle but I can see a few flaws. I personally have a set of bathroom scales next to the toilet and find it easy to step on before hand, and step on again afterwards. That gives the same result without having the extra expense of having to purchase a new seat.
I cunt a4d that...
That said though, I would still get a skewed result, as it wouldn't take into account when I go in the bed during the night or when I'm sat watching TV or at my desk, and I'm too lazy to bother getting up etc.. So overall accuracy wouldn't be that improved for me anyway...
