I had the pleasure to speak with Scott Neyedli on Saturday who has been sponsored by On for 2 years now. I was asking about wear, due to the high cost of the shoe, he tells me that early on there were issues but these have been resolved with a better compound and attachment of the sole.
He recommended CloudRunners for the day to day and CloudRacers for eeerm racing. He also mentioned (as does the website) that you need to drop a European size (half UK / US) when switching from the Runner to Racer so a 42 Runner would be a 41 Racer despite it being the same mold, just the thinness of the upper.
Worth a try - they do look cool too