well
to tell the truth, i haven't had too many passengers on the back since i lowered mine the 3 inches and all. now, if i have any passengers, i can't go over bumpy stuff without bottoming out in the rear. aside from that, though, as long as you haven't lowered yours as much as i had to (i'm short), then there shouldn't be any problems with that. depends on how much your passenger weighs, and whether or not they ride like a sack of potatoes.
as for how it handles in the turns, you have to make sure your passenger leans with you, or stays upright---they can't go leaning away from the turn and you or they'll mess you all up and then you're both screwed. they pretty much have to be like an extension of you, do whatever you do, that kind of thing. and it should be someone who isn't afraid of how you ride, who's had time to get used to how you ride and knows what to expect.
that said, you should take the time to get used to having this person, or people, ride with you so you know the kinds of reactions your bike will have in different situations----how far you feel comfortable pushing it, etc.
of course the bike will take longer to stop, of course it won't go as fast as it would otherwise, it'll probably sink into turns a little quicker and take just a little more to pull out. it's all just stuff you have to get used to for your own self.
good luck, though, and have fun. :cheers