Yes, since my drawing isn't much better than OotS on a good day I use downloaded art extensively. I then use it in my houserules doc, handouts, counters, etc, lots of things.
In fact I do regular searches of art sites like deviantArt and Elfwood to catch potentially useful art, I'll swipe entire galleries if they're especially high quality. I've got something like 20,000 images on my HD because I'll leave a spider to grab keyword tagged pics for me while I'm at work, when you draw as badly as me any usable art is a godsend.