I've done it 3 times. The first time I had a vaguely "out of body" feeling, but was fully aware that it was just the salvia. It lasted about 3 minutes, then I laughed uncontrollably for 10 minutes.
The 2nd time, I laughed uncontrollably for about 20 minutes, and just felt kind of tingly.
The 3rd time, holy shit. I completely lost any sense of time, I felt like time had either stopped, or sped up, or started moving in reverse. I would blink and imagine something and be totally engrossed in my imagination, thinking that years had passed, but it was just a blink. It messed with my senses in ways that I'm not even going to try to explain. It was incredibly intense, and at times, downright terrifying, but I learned a lot from it. Overall, I'd say it was positive. (The 3rd time, I didn't feel really normal again for almost 2 hours, which is crazy long for salvia.)