Most helpful - thanks
I found the following information on the pocketgpsworld site
All Garmin systems are currently based on Q2, 2007 map data from Navteq and is therefore approximately 12-18 months old.
The surveys that are carried out by the digital map suppliers, Navteq and Tele Atlas, are time-consuming and laborious and it is near impossible to ensure everything new is included in a survey. Both these companies drive the length and breadth of the country to digitise roads and capture as many features as is practical. If a new road opens in an area a day after a survey was conducted it can be another 12-18 months before it will be in a map update for a sat-nav device.
As a general guide, it is typical that the map data on your sat-nav will be at least 6 months old when you purchase it simply because of the time it takes for the GPS manufacturer to test the map data and convert it to the manufacturer's proprietary format. Also, each GPS manufacturer has their own production cycle so release dates and the map updates are different, so one GPS system may have the most up to date maps today but this will be replaced by another GPS in 3 months time and so on.
Q2, 2008 Navteq map data will be available in new Garmin models from October (Mapsource City Navigator Europe 2009) and as an map update in January 2009.