I have been using a Trascend 4GB SDHC Class 6 card for about 2 weeks now with no problem. I put my NA map with larger POI (from GO920) and it is working flawlessly. There are no lag time what so ever when navigating.
I'm in the process of creating my own POI. I have a .csv file with all the lat/long, name and telephone number. How can I add "Details" info that shows the address just like some of the factory POI on my GO720.