I've done this twice... The second time was punishment for not writing here the first time, heheh. What can I say? It's uncomfortable dry and it's uncomfortable wet. Really, I found the sensation to be worse than having sand down your pants and for those who know, that in itself is very unpleasant.
The kitty litter only really slowed the process of filling the diaper and didn't exactly help keep me dry. I got kitty litter in places I didn't even know I had and it didn't really turn to mush when wet... Well not for me, at least. It got a little softer, granted, but not that much to tell the difference. All in all, I found that punishment to be quite uncomfortable (very effective) and I really wouldn't like to do it again.
Thanks for the punishment idea, Dipered Slave!