There was a thread on here a while back about using menthol ciggies as baccy for joints.
The menthol in the cigs opens up the airways in the lungs - this is why smoking menthols is worse than smoking regular cigs. However, if you mix menthol baccy with some Herb, the airways will open up more and, yep, you guessed it... the THC will be absorbed into the lungs quicker and easier, so you will get higher.
It also tastes pretty nice too.