I stick them to the case only if they are useful.
As for example, once I got a motherboard sticker with the name model writen on it, so I added it to the case, because is useful to know the model without opening the case, or downloading CPU-Z.
Some Intel motherboars include a sticker with detail of jumpers, an motherboard components (jumper to reset bios, batterie location, same channel memory slots, etc)
Is useful when you manage lots of machines, and reinstall windows.
but generally, I don't like to paste trash on the cases. I think that is bad taste to make free propaganda. And when you change the mobo, you need to remove those crap sticked.