Here's a study about flaxseed in banana nut muffins

Eating quality of banana nut muffins and oatmeal cookies made with ground flaxseed
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The purpose of this study... was to describe the palatability characteristics and overall acceptability of banana nut muffins and oatmeal cookies prepared with ground flaxseed. Such information can be useful to dietetics professionals who recommend this substitution to clients.
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Findings suggest that using 30% to 50% ground flaxseed will produce acceptable oatmeal cookies and banana nut muffins that differ little in sensory attributes from those made with all-purpose flour. Flaxseed flour is worthy of use because it is a source of [Alpha]-linolenic acid and soluble and insoluble dietary fiber. Flaxseed is available in most health food stores in the United States and Canada, in a few supermarkets, and from food brokers providing specialty grains to the food industry.
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The shelf life of whole flaxseed is indefinite; however, ground flaxseed should be kept frozen as it can become rancid within 1 week at room temperature.

Alpers, Linda, and Mary K. Sawyer-Morse. "Eating quality of banana nut muffins and oatmeal cookies made with ground flaxseed." Journal of the American Dietetic Association 96.8 (1996): 794+. Culinary Arts Collection. Web. 16 May 2013.

Good to know flaxseed flour goes bad so quickly.