Apparently digital currency is all causing a problem in tipping and donation. Can't put a dollar in the old man's hat if you don't carry a dollar any more. And tipping at bars etc can be harder too.
That being said, I've not given money to an homeless person in ages. Whenever asked I simply answer "I only carry cards, sorry" and they immediately lose all attention towards me.
That's not too much of an issue in Europe.