I have the Keen sandals, and used them with SPD pedals for a couple weeks. I changed out my pedals, so took off the cleats, but still wear the sandals. I think the Keens worked great on short rides around town, but I don't think they offer enough support from mid-foot to heel if you're riding for more than 20 miles. I do like them as sandals, and have gotten compliments on them when just walking around.
2013 Kirk Frameworks JK Special/Selle Anatomica
2012 Gunnar Sport/Brooks B17
2001 Calfee Tetra Pro/Selle Anatomica
1984 Raleigh Sport/Brooks B66