Arduino smells burnt but works fine, what shall I do?
You probably hurt something. But keep using it until it dies. :-)
Did you try to power it from a non-USB source? You could have done some damage to your voltage regulator.

I recently burned a trace on my board. It popped right out of the board, let out the magic smoke, and made me scared I had fried the whole thing. One bus wire soldered to the right place, and I'm back in business. Pictures of the issue and the fix are here. Good luck.