I been shooting in RAW since I got my DSLR about a year ago (why not? storage space? that gets bigger and bigger all the time) and I kept storing my pictures in iPhoto, but this week I moved to Aperture. I read in a blog post that the first thing someone did when moving to Lightroom was re-white-balance all pictures (or however you call it, I'm not even a hobbyist when it comes to photography). I am wondering if I should do the same, can anybody tell me? and if so, how is it done?
It depends on how you shot the files originally. Did you shoot with auto white balance in camera, a custom setting, or a preset? If you always shot with a certain preset or custom setting because you planned on modifying the white balance later, then you may benefit from a mass auto adjustment. If you used auto white balance, I doubt the mass auto adjustment would gain little if any improvement. If anything I would imagine it could cause more problems that you would have to fix when it reads it incorrectly.
The real benefit to white balance adjustment in post production would be the added knowledge you have of the situation and how you want it to turn out, so if you just are doing a mass auto setting, you really aren't using any of the advantages. It is beneficial that you shot in RAW originally, but I would leave the files alone unless you want to dig in and fix the images setting by setting(because that is how most white balance is set).
It should be noted that often white balance is a matter of taste, or matter of pattern recognition, ie. not possible to do without human eye. For example, if the scene has both incandescent light and daylight, like in a room with lights on and a window, it's often matter of choosing which one to use. Or if you shoot in daylight, but frame the image so that only warm-colored items are showing, any automation will "correct" the colors to a lot cooler variants.
Raw photos are not white balanced, however the metadata and of course, the embedded JPEG preview will contain some white balance setting based on the camera settings at the time. It may be an automatic white balance, day, night, cloudy etc. This will most often be honoured by default in the program, however the other development settings may not (contrast, brightness, saturation etc).
Both applications should be colour profile sensitive, and possibly be using the same raw conversion engine.
I would say it's not necessary.