There are two distinctly different categories of nav software for laptops.
One is programs that seem to be primarily planning programs that have had navigation added. That's Streets&Trips and Street Atlas. Both are rich in features for sitting down at your computer and planning trips and complex routes with multiple stops. The nav features are not what you would expect if you've ever used a personal navigation device like a Nuvi or TomTom or Magellan.
The other category are primarily nav programs that have features that can be used for trip planning. That would be programs like Mobile PC, iGuidance and Navmii. They look just like a Nuvi/TomTom/whatever that you loaded into your laptop. The nav displays are great. The trip planning features are all there but not nearly as enjoyable to sit down and plan an extended trip or complex route.
We don't have North America maps for Navmii yet so it's hard to say much about it other than it looks pretty nice so far. Navmii, iGuidance and Mobile PC all have great nav displays. I would give the edge to iGuidance simply because you have a choice of two displays. There's a standard PC display and there's a "UMPC" display. On my netbook the UMPC display is great because the font and icons are easy to see.
On the other hand I prefer Mobile PC overall because I prefer the user interface and I like that I can get maps for anything and everything I might ever want and it's easy to add them to Mobile PC.
All three of these nav-oriented programs will make excellent use of a touch-screen if you have one.
I don't know if that helps any. If you have any specific questions about things that are important to you, just ask away. I may not be able to answer them but I'm sure someone can.