Went clipless about 8 years ago -- SPD clones first, then the real deal. For a week in '04, I had to go back to platforms (clone gave up before I was financially ready to upgrade), and I NEVER DEALT WITH SUCH CRAMPING PAIN IN MY CALVES IN MY LIFE!
Now I'm on Time ATAC's, and will never change -- I have three sets, and am looking for more, JUST IN CASE...!