you should try and get a 3.0 because otherwise it becomes very difficult to get through to grad school and all that.
but once your through the door it doesn't matter, what will matter is your understanding of the material. I'd like to see the poor sap who tries o tell his advisor "but, I came in with a 3.8"
also a year or two after your out of college nobody will care what your grades were, just how smart you are.
EDIT: also people on this forum seem to believe that its a linear model of going to college, going to grad school, and then gettig a good job because they had good grades. That is a very boring life, if your feeling a bit buned out take a year off and do all the things you've been wanting to do. Be a ski bum, see the world, join the peace core. My father decided that he wanted to be a ski bum after college and lived in new hampshire for a year, then he spent the nex decade doing strange and interesting things around the country, including livin in a trailer. Now he's the head of sales for a major cosmetics packaging company, and handles millions of dollars worth of sales. Same thing happened with my step-mother, she didn't get serious about her career till she turned 30 or so, now she's the director of purcahsing for a very major cosmetics company.
life is not a linear progression, and they're are some things that you can only do when your young, if you want to do them go out and do them. You have your whole life to become a phd.