I tend to shudder when people talk about bitcoin being "cheap". There's a massive amount of energy wasted to maintain the public ledger. It became much more clear to me how this impacts the cost of transacting bitcoins after reading this article: http://letstalkbitcoin.com/blog/post/how-many-bitcoins-does-...

...and particularly after seeing this graph: https://blockchain.info/charts/cost-per-transaction

I'm more excited about proof-of-stake, as there isn't this arms race to throw more and more computing power to generate bitcoins. I'm not sure why it hasn't seen more adoption, but I will admit that I don't pay a lot of attention to the cryptocurrency space...