Last October a website called BTCBurns.cf identified 397 burn addresses containing 2,657.8686 BTC lost forever. It has gone offline. Since it stopped keeping track 26.04 additional bitcoins have been sent to these addresses.
The total number of unspendable bitcoins is now 2,771.4086.
http://bitcoinwhoswho.com/blog/2016/12/21/btc-burn-addresses/Thats really painful part that we are destroying bitcoins. I always believed that there are some better ways to avoid processes like proof of burn. Even if such activities are increasing the values of remaining bitcoins, I dont think that it is a wise idea to use it. Bitcoin is in initial phase and we shouldn't do something that might affect the future such as destruction.