How would you react? Happy?
You might mention it to others. You would write more brilliant comments. You would feel appreciated, it's a great feeling.
What if I paid $20 into your PayPal account?
It's just become work.
How much will you charge next time? Will you work less if you don't get paid? Will others now want to be paid?
Money makes communities implode. So send flowers, fruit baskets, chocolates and invitations to special events. Surprise gifts bring out the best in people, money brings out the worst.
Note. Read Dan Ariely's Predictably Irrational - It's a brilliant book and tests this theory beautifully.