Do you mean that your GPA will be a 3.6 for the semester or cumulative? If the first, there's nothing to worry about. Don't bother bringing it up in any essays or interviews. If the latter, this isn't that bad overall, but a semester that brings your cumulative GPA down from a 3.8 to a 3.6 would probably concern the adcom and might be worth explaining briefly in a secondary essay. I had an incomplete during a semester when I struggled with depression, and my grades were lower earlier in college because of a variety of family and social factors. When I touched on these issues in my essays (which was very brief and indirect), I tried to be discreet, emphasizing how I'm learning to cope, how my grades as a whole are rising, and how through my difficulties I've gained a greater compassion for people. If your cumulative dropped from a 3.8 to a 3.6 in a semester, be discreet if you mention it in primary or secondary essays and be ready to explain the trend in an interview without sounding like you're making excuses.
that could easily happen to anyone and not for any bad reason. i mean what happens if for one quarter you just happened to have one really crappy teacher who seemed out to get you or you just took a lab that has extensive lab report requirements which is your weak spot. don't bring it up as it could only hurt you and make you seem like someone who thinks a B+/A- average for one quarter is the end of the world.
I wouldn't worry about it. I'd say you'll be fine... although I can't say for sure because of the fact that I never got lower than an A in any of my classes. My professors loved me. We even used to hit some clubs together. I'm pretty sure I would have got an A for grinding ability as well.