My take on the GPS business is that it is going to need to make a dramatic turn to allow live on-line data to be accessed or the phone mapping programs will simply run away with the market. I was just in San Marcos, TX and one of the streets had been under construction for 2-3 years and traffic could only travel in 1 direction with a detour to a street a block away to travel the opposite direction. My phone (Google Maps) knew that 2-way road could only be traveled in 1 direction and gave the appropriate detour. I had only been there a couple of days when the construction was cleared and the road opened in both directions. For about a week Google insisted you could not travel on the newly open road but one day I entered a course that included this road and it showed a route that included traveling on the previously blocked side of the road. I am not sure how they managed but this would simply have been an impossible feat with a stand alone GPS.
If you think you also like the GPS units traffic option, Google is now using WAZE updates for live updates and will actually do a live re-route of your trip should this cut down on your ETA. I discovered this in Austin, TX when it said to continue on the side road for 3 miles instead of getting on the Interstate (the obvious route). I shrugged, called the GPS stupid and headed for the on-ramp. Luckily as I pulled onto the ramp I could see traffic at a stand still and pulled back onto the side road driving past miles and miles of traffic.
If you haven't tried your phone (assuming you have a smart phone) I highly suggest that you do before you spend any money on any GPS to see if it meets your needs.