I have never seen issue in this subject either.
After I got my PPL a thousands of hours bush style pilot friend of mine came flying with me a lot. It boosted my confidence, nav skills and short field and near MAUW flying skills no end. he also took me flying a lot in really crap weather conditions to show me how bad it really has to get before you need to go IFR.
Since then I have taken a PPL student up with me on quiet a few occasions. It definiatley boosted his confidence and nav abilites as well. depending on the airspace and weather I either let him navigate or fly (from the right seat), I have not let him do both yet.
I personaly think it is a great thing to be going on.