I am fairy new to marketing, practicing over the last 5 years, so studying is a constant past-time of mine.
In my reading however, I do not think that selecting the segmentation scheme for your business is given enough attention. Segments are lenses through which I evaluate a product's success or failure in terms of design. If segmentation does not deliver an easy-to-follow framework for explaining buying behavior, then it does no good to product managers.
Beware of the segmentation strategy that serves marcom - while knowing that I am female and 31 may make it easier to communicate with me, these demographics do not define my purchasing behavior. I will not buy widget x because I am 30 something and then switch to buying widget y when I am 40 something, just because of the change in age.
Are you segmenting based on characteristics that have a direct, causal relationship with buying your product? If not, I highly recommend reading "Finding the Right Job For Your Product" MIT Sloan Management Review Spring 2007 and reviewing your segmentation strategy.