They are way too volatile to be any sort of 'currency' imho. and are just another speculation,
as a store of value for commerce..volatility is not good.
Add in all the other negatives.... oh and Etherueum just did more jigglez ..hahaha!
http://www.marketwatch.com/story/ethereum-has-lost-175-billion-in-market-value-in-4-weeks-2017-07-11