Not a fan personally.
I umm'd and ahh'd about different Head Units....... dismissed the RNS as I'm really fussy about sound (it's also my job!) and went for a Pioneer F900bt.
The *only* nice thing about the RNS, I think, is the built in hard drive.
The satnav aspect didn't blow me away.
Sooo.. the F900bt. Uses Igo8 satnav..... and I really like it!!

Full postcode search, Traffic Management, up-datable speed cameras. Been using it in earnest for the last month and I have to admit there hasn't been any issues.
It locks into my iphone via bluetooth and the addresses also come up.
Gives a great overview of the trip too.
And after being a devoted TomTom user for a great many years, I found the transition to a new satnav quite easy, and using other satnavs, it does highlight the failings of TomTom.
I've also got a GO540, and am running CoPilot Live 8 on my iphone..... and despite the GO and iphone being shinier graphics at times (although OS3 does address this somewhat), it's rock solid.
So, the moral is IF you can live without the OEM look (which imho, if I'm spending alot of money on a stereo, I WANT to show it off!), DO look elsewhere.
The Kenwood stuff is quite OEM too, and Pioneer, well, I just like the sound.
Hope this helps (as an alternative view)
Dan