I have tried this stuff and not that I am a very experienced drug user but the intensity was far far greater then that of mushrooms. You experience complete ego death, you have no idea who or what you are. You go into a different world that can be made up of anything, even things you didn't know existed. There is no language in this world yet things are communicating with you. You will lose conciousness. You will feel extremely anxious and paranoid and "dirty". I haven't known anyone personally who liked this drug in any way, shape or form. I'd say stay away. I was very scared and it came to be one of those moments in my life that I will never forget.
Personally I do not see how anyone could possibly become addicted to salvia, but I guess its possible.
Check out http://www.erowid.org for unbiased information.