Proper white balance is very easy to do in post-processing. If you shoot in raw format, it’s even lossless. (This is one of the best reasons to shoot in raw format.)
More than anything else, improper, too-yellow white balance is the most common flaw that makes me cringe when looking at photos I took a few years ago.
As a general rule, if you’re shooting indoors with auto white balance, your SLR will almost always choose a level that’s too warm. If your indoor shots are always tinted yellow, this is why.
You don’t need perfect gray-neutral white balance on every shot. It can often make indoor scenes look unnaturally blue or sterile. I shoot on auto-white-balance in raw, then adjust in Lightroom by using the eyedropper tool on a neutral area and then doing a slight manual adjustment (usually a bit warmer than Lightroom’s guess). Any reasonable editing program can do this, including iPhoto, although iPhoto won’t do it losslessly with raw files.
Use white balance consciously as a tool, rather than letting your camera guess.