I have several different types of Keen shoes (Newport sandals, Taos shoes, and Targhee shoes). For all of them, I had to order a half size smaller than I would usually take. I usually take a size 9 shoe, but in Keens I am a size 8 1/2.
I think it may have something to do with width. My feet are very narrow, and Keens have a bit more width than most shoes.
I love my keens! They have GREAT arches.
But the "bumper toe" is not the best for biking if you already have a bit of "toe clip" when you ride.