I'll add my 2p here. I'm not overly convinced about the RNS.
The MAIN advantage for going RNS is that it looks (and is) totally OEM.
Personally, I've gone for a Pioneer F900bt (now been superseded by the F910) - better Ipod interface, based on I-Go satnav, built in Bluetooth for phone.
NO built-in HD for tunes, but you can put your own HD onto the USB connection.
But for me, the big one is the sound.
I'm sure RNS is a great box, but imho, if your spending that type of money (+ the bluetooth module AND MDI for ipod?), it's a LOT of money for what it is.
Plus it's much easier to put your own amps etc onto with an aftermarket machine.
The other pro of the RNS is the integration into the VW's highline and MFSW.... that is nice. But I don't have either (nor do I miss them).
Aftermarket all the way
Dan