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I would tip $ 0.10 for a great comment . Imagine if there is 10 people willing to do that too. That comment earned $1. Now if this person post 10 great comments per day that's $10. The few cents can build up pretty quickly :)
Even if 10 users only tip $0.01 per comment, that's still $0.10 cents per comment, multiply by 10 and that's $1 per day which is $30 per month for commenting on a forum!
I'm sure you will be surprised though how much people are eager to tip, especially if you throw a competition into the mix.

Exactly. Even if you post earns 1c you generally don't get it and that can discourage new people. My votes won't pay much, but I am willing to do tips

I'm sure you will be surprised though how much people are eager to tip, especially if you throw a competition into the mix.

I imagine that if people were that eager, we'd be seeing a lot of such manual payments on the blockchain already?

Tipping needs to be as easy as upvoting for it to be used. If it takes more than 2 sec to do then people won't do it.
People buy a lot of apps on the app store because it's seamless, if they had to enter their card details everytime they would buy a LOT less apps.