If you like the Nuvi interface, you would probably be happy with Garmin Mobile PC on an Acer Aspire. The interface is virtually identical and you get a bigger display.
The downsides are;
No touch screen - Mobile PC is optimized for a touch screen - fortunately most functions have a well marked keyboard shortcut.
Brightness - Nuvis are optimized to work in brighter environments. Netbooks aren't
Speaker volume - even in my noisy truck, I can hear the Nuvi. Of course if your signature means you have a BMW, you might be able to hear the Acer.
Mounting - You will have to place the netbook somewhere you can see and control it
Upsides;
The netbook is a computer so can perform a lot of different functions
The netbook has a real keyboard
The netbook lets you try a variety of navigation programs even at the same time if you are so inclined
Cost of the netbook plus software is well within the price range of a better Nuvi.
My personal opinion is locking into a 2 year data plan to save $300 or so is not a good idea. However, I can not know your situation. Investigate the cellular data plan if it meets your needs. I think a netbook with a screen size you like and Windows operating system will get you started in the right direction. Then read about the different navigation programs we discuss to see what interests you.
Terry