I voted this up because it's a reasonable question. I was recently answering a question about the difference between:
- It really is pretty.
- It is really pretty.
My position is that there really isn't a difference -- and there isn't really a difference. So, you can't do it with very, but you can do it with really.
Hmmm. In my version of English, there really can be a difference.
- It really is pretty — I expected it to be ugly, or ordinary, but in reality (really) it is pretty.
- It is really pretty — "really" is more or less "very". It is quite / very /seriously /a lot pretty.
But this distinction isn't really reliable.