Salvia is the latest in LEGAL drugs that are for sale in the USA..
It's a very dangerous drug IMO and causes the user to experience highly dissociative hallucinogenic effects similar to PCP or shrooms.
While the effects are not normally long lasting they can be severe and extremely debilitating..
This stuff is no joke and can cause folks to loose it. If used while driving IMO it would be worse than any of the other recreational drugs out there like pot or alcohol.
There also may be other side effects with excessive use such as depressing vital functions like BP and putting users at risk of death--but I have not seen any studies in this area.
This stuff should be controlled and folks, esp parents may wish to keep a look out and be aware of its easy and LEGAL access and it's rapidly growing popularity among young folks..
Here is a kid attempting to demo how the effects manifest while driving.. The video says it all and trust me he is NOT acting--imagine if he was already driving when he took his hit, or someone passed him a joint.

http://www.youtube.com/watch?v=Sp2V6NXCkE0