Having had several Audi Satnavs in recent years (all RNS-E for those that care as opposed to the latest 3G MMI in the 2010 MY A5s) I can honestly say that the TomTom is a heap of useless junk in comparison (I have a 540 Live, about 3 months old). Just everything in a TomTom is inferior - even the 7 digit postcode search which should be excellent is a let down. The Audi offers just 5 digits and then a list of different categories in the vicinity of the destination - absolutely superb in the real world. And to cap it all the 540 Live reboots itself once a day as you are driving along - a known problem apparently.As for Sat Nav... a choice between £1550 or £1950... I just can't see it... I have a TomTom already which is fantastic and hasn't let me down and it cost less than £300. The built-in Sat Nav's just seem overpriced for what they deliver. If it was say 500-600 quid for something that was essentially integrated then I might well be tempted but £1500-£2000, I just can't quite stomach it. As mentioned I saw the blast posted by another user earlier.
The Audi system is a bargain - honestly it is.