Yes a few people have.
Its not a wise thing to do in bitcoin though.
I understand the wisdom of it. Fiat money relies on usury. CB's need to print more money to satisfy repaying the original loans. My question is if bitcoins start earning interest, where will this extra money come from to pay of the principle?
It shouldn't be necessary to charge interest...Bitcoin's value increases over time, so there could reasonably be loans for 0% or negative interest.