I thought I'd offer a quick review of the Volkswagen Premium Bluetooth and the RCD510 radio. The radio is an extra £220 (in a Passat), the bluetooth is £575. Both fully integrate and work with the multifunction steeering wheel. Overall, the whole system is fantastic, but the problems are so frustrating that I'd not go the same route again. Read on.................
The RCD 510 gets a complete thumbs up, with no complaints at all.
Colour touch screen control, 6 x MP3 CD's, tags visble on screen, track listing etc. There is also an SD card slot, which works brilliantly and an AUX-In 3.5mm socket in the armrest. The radio isn't bad either, reception is good and you can store 35 stations as a mix of FM and AM without swapping bands. Tracks and radio stations are shown on the touch screen and on the highline display. There is no longer an option for iPOD integration, but it was pretty krapp anyway, so I don't consider it a major problem.
If you have the optional front and rear parking sensors, these are also integrated into the radio and a "view from above" graphic comes up on screen as soon as reverse is engaged.
The German version has the option of park assist, but this is not for UK market yet.
The Premium Bluetooth kit fully integrates with the radio, the highline display and the steering wheel. Overall it is magnificent, allowing full visiblity of contacts lists, on-screen speed-dials, integrated voice dialing, easy change from phone to phone. It is not like a Parrot or similar kit, in that it doesn't just control the phone; it is a fully integrated car kit that "steals" the identity of the SIM card in your phone and then does its own thing. It uses the car aerial, so reception is always perfect, even on the top of the Pennines where I usually lose signal. No cradles to get gummed up with bits of dust, the phone can stay in your pocket unless you need to plug in a charger.
However, the Bluetooth kit has one MAJOR flaw. It can only work in this fully integrated mode with phones which are compatible. It cannot offer a "simple" bluetooth mode like other car kits or like handsfree earpieces do.
The list of compatible phones is very short and most of them are now obsolete. Samsung and LG do not support it, Sony Ericsson and Motorola did, but now do not, so maybe your old phone will work but your new one definately will not. A range of Nokia phones do work, but I've tried a couple of supposedly compatible old 'uns and the connection results were patchy at best. It also turned its nose up a a new N95 but this will supposedly work if you do a software patch to the phone. A couple of Siemens phones also work - great if you live in Germany but no use here. If you've just bought a non-compatible phone on an 18 month contract don't waste money on the VW kit because you are going to be using the Borg headset until you swap to a Nokia. 
Nokia can't/won't guarantee that their phones will support it in future, but given that they supply the kit to VW the chances are that things will be okay. 
So, in summary:
RCD 510 = 10/10 (lower marks if you are an avowed iPOD junkie)
RCD510 with reversing sensors = 10/10
VW Premium Bluetooth Kit = 5/10, reflecting its deeply flawed genius and its Nokia fetish.
I hope this helps.
p.s. apparently, it is the same phone kit for VW, Bentley, Audi, Skoda, Porsche and Ferrari 599GTB so if you want to use the same phone in your Ferrari, there is only one model you can buy from Marenello, don't buy a 430 or a 612.
