How loyal are you to one airline? Perhaps it can be measured by what percentage of your air travel is done on that airline, versus any other.

For me, my most frequently flown airline over the past several years is probably only about 20-25% of my air travel (there are three airlines that are about that level for me -- AS, WN, UA). The rest has been scattered among many others: NW, LH, B6, AC, CP, CO, DL, AA, and a few others I don't remember.