Yes, I've done it a few times. The experts say that it is not a good idea because the higher gravity stresses the yeast, but I didn't notice any problems.
Disclaimer. Just because I didn't notice any problems, doesn't mean that there weren't any. It just means exactly what I said, but I'm usually fairly good at noticing off flavors and fermentation problems.
P.S. The only times I've done it were when I was making another beer with an OG > 1.070