The traffic stuff (uses TMC from itis) is quite good on the RNS-510, the display on the map with the symbols for the type of delay is one of my favorite features. 
TMC actually uses two sources in the UK - TrafficMaster, which uses live "real-time" data from the blue poles (and other monitoring sources), and ITIS who provide iTMC data. The ITIS/iTMC is a flawed system, in that it isn't real time, it isn't fully automated, and relies on "human intervention". ITIS only collect their data from National Express Coaches and Eddie Stobart trucks - so if a truck/coach is on a tea brake or scheduled bus stop, you get flawed data, and if there are no Nat Express or Stobart wagons on your road, you get no data. I've been caught out twice recently - one for a hold up of 20minutes stationary traffic, and the other for an 8 mile v.slow (less than 5mph) tailback - both on "trunk" roads. One work around is to manually use Classic FM as the TMC source (because that carries the more reliable TrafficMaster data), but Classic FM isn't always available (signal not strong enough to correctly carry RDS data) thruought the UK.
Audi have been using TMC since 1999 Europe-wide, and included the UK around 2003, and the RNS-MFD2 also uses TMC in Europe - but Volkswagen were too tight to pay for the UK TMC license on the V3/2006 disc,
though they did include on the later one.
Anyone who has used the dynamic navigation (from TMC alerts) in Europe, particularly France and Germany, will know that their use of TMC is considerably better than here in the UK.
