I've had an arch rim on the rear for the last 4 months or so. It's been great so far - nice and light, no dinks or dents and still true. I'm running it tubeless on standard tyres with a stans rimstrip.
Nick - the arch rims can be used without a rimstrip with the right valve but if you're intending on using normal tyres then I was advised to use a rimstrip as well. There's lots of info on the justridingalong site and I spoke to Jon there who was very helpful.