There are many thins that could be useful as a way of proving date or making a mark on a public ledger. Shall we list all of them?
You used bitcoin as an example because of your fanboyism. In no way is it obvious to use a currency or it's surrounding infrastructure for this (non intended) purpose.
It's nice to see a company that spent along time building a solid product that has added value to many business around the world.
A nice change from the stories we hear about startups racing to release something of little real value and trying to sell themselves as quickly as possible.