I used to have a TOM TOM. I have used a Garmin (older one about 3 yrs ago). And other than the interface (touch screen rocks) I have not had any problems with the navi in the V.
I don't know where you guys are using yours but I have used mine from OH, KY, TN, FL, NC, SC and VA with no problems yet. Of course I don't get off the highways much except in the city. With the exception of a new section of interstate that was built a few miles from my house in 2004 and a few subdivisions that are new, mine has all the roads I need. It gets me from A-B, helps me with my ETA, leads me to gas stations, dealerships, stores, restaurants AND hotels.
Besides the interface, just what does your Garmin/TOM TOM do that is so special?