As of 2014, Bitcoins have definitely went down which suggests that it has failed as a digital form of currency. However, these coins are just more than that. This technology is still going through a major change where these bitcoins will still be used to undertake many commercial transactions.
failure means that no one ever will transact with this coin and its community has disappeared. Also if a major bug or failure in its design that cannot be repaired.
Ups and downs in its value, is not an indication of failure 
the down in value is just an indication that people’s attention has turned also to other interesting projects and ideas but progress and strong community are still there.
people were saying it failed in 2010 when it went from $32 down to $2. :))
Maybe the same for Peercoin with that $0.5 price? 