For no reason other than trying to understand *why* you'd want to try this, I played with freelensing today. I can definitely see the appeal - I got some fun, pretty and interesting shots, but also a whole lot of wacky blurry ones. This was one of the sharpest, and it's still a bit softer than I'd like.
To be fair, I'd probably have had better luck with the focus if I'd read through this tutorial thoroughly before trying it. I was using my 24mm lens instead of something 50mm or greater. Guess I'll have to experiment more this weekend!