I agree - DS is 8 months old and I found that if I give him something to play with while nursing, he stays latched MUCH longer. Sometimes I wear a necklace he can play with and sometimes I just give him a pacifier to hold that he sort of fiddles around with...it made a huge difference.
As far as the lunging, DS also does this. I notice that he does it not just at my breast, but at his toys too....I think he's just testing his depth perception and I think it's a game for him...sometimes he even makes a "aaarrrgh" sound as he does it. I also notice an increase in this behavior when he is overtired or gone longer in between feedings.
The only behavior I correct during nursing is biting...which has become a generalized problem anyway, so we're working on that in all aspects.