Let's take a scene with a giant oak tree in it. When you first start the panorama, the oak might be out of the shot. As you move the camera to frame the next shot, the oak might now be in the shot just off the center of the image. The metering system sees all of that dark oak bark and figures that it should open up the iris a bit so you can see more of the bark. The same could be said about auto-white balance. As you continue to pan and take more images, other bright and dark objects could move into the scene and affect your exposure.
Instead of using auto exposure and auto white balance, use manual settings. Take a few test shots panning across your scene and look at your images to determine the optimal settings (these might be a compromise). Delete those test shots and start shooting.
You might consider a stitching program like ArcSoft Panorama Maker, software dedicated to blending images together for panoramics, which can help when the separate shots aren't perfect.
One final tip: When I shoot a series of panoramas, before and after each sequence I take a shot covering the lens (I get a black image). After I download the images to my computer and browse my thumbnails, I can see where each panorama starts and ends.
Family Photo Issues
Q) I'd like to get a camera for my wife. I already have a digital SLR, but she says it's too much to use for snapshots of family events. Recommendations?
Via seat 12B
A) Okay, so this isn't a real letter, but it's a real question, asked by several people as I flew across the country. My seatmate would ask about what business I was in and the conversation would lead to the inevitable camera recommendation. Rather than blurt out a model number, I like to ask a few questions to find out their photography interest. And while I don't make model recommendations, asking questions can help point to a camera type.