New with a question

Typically you'll want to keep each day's calories separate. Don't try to make up for a deficit or overage on the next day. Eating too few calories one day won't automatically launch you into starvation mode, and eating too many won't cause you to immediately gain back all the weight you've lost - as long as you don't make either of those a habit.

I would recommend that you avoid micromanaging your calories. As long as you are staying reasonably close to your goals and exercising regularly, you should be just fine. If you feel hungry, tired, or like you're eating too much, THEN you should reevaluate - absolutely be sure that your calorie intake is primarily from nutritious, whole foods, that your macronutrient (fat, protein, carbs) intake is balanced, and that you aren't using calorie deficits as an excuse to eat unhealthy foods. If you want to indulge from time to time, that's fine, just plan ahead, be aware of what you're eating, log your calories even if you know you're going over, and don't feel guilty about it!

Personally, I like to underestimate my exercise calories because I know that everyone, even those of us with the best intentions, can accidentally underestimate our calorie intake. (Check out http://www.youtube.com/watch?v=JVjWPclrWVY). Restaurant meals can often have as much as 18% more calories than listed in their nutrition guides, and people can easily say "Okay, that was 1 tbsp of peanut butter" when it was actually 2.

Ultimately it's different for everyone, but the short answer is "No, don't roll over your calories." Good luck and welcome to MFP!