If the mistake is "glaring", I will fix it; otherwise, I don't do anything. You know the old "galloping horse" thing...
Once I made a double Irish Chain quilt. When I picked it up from my LAQ, she said "are you trying to be Amish?", and said that I had one row of blocks turned wrong, which she hadn't noticed when loading the quilt, but did when she quilted that particular block. It took her about 15 minutes to find it again to show it to me. Even now, I still have a hard time finding that one block, but it doesn't take away from my enjoyment.
I say if the recipient will love it either way, give it to her, and let her enjoy the one you made with such love.