I'm gonna put a fly in the ointment and say the Pioneer F900bt or F910bt. MUCH cheaper and you've got the options for putting subs and amps onto it.
The Kenwood is roughly the same price.
The Pioneers have built in GPS/Satnav, BT, and a GOOD ipod interface.
The advantage of the RNS is purely one of OEM looks (imho) - the HD transfer of mp3s etc is good, but nothing that can't be done by other options.
In the RNS's defence, I have yet to hear one - it may be VERY good, but I personally like the warmer sound of the Pioneer stuff.
Just IMHO
Dan