Well, I'm going to play my usual contrarian role here, just for a little advocacy for the devil.
If you just want basic navigation and not a lot of extensive trip planning features, and if you want it to be quick and simple to start up and use, the laptop is not the way to go. For simplicity and flexibility for personal navigation, a handheld personal navigation device is so superior to a laptop that there's no comparison.
Think about the type of vehicle you have and how difficult it may be to position a mount for the laptop so it is in a position where you can see and use it safely and effectively. If you have a vehicle smaller than the average pickup truck or large SUV (and a partner who objects to sharing part of the passenger space with superfluous hardware) you may find it impossible to position a laptop so you can use it safely and effectively.
Think about the time it takes to secure the laptop in its mount, turn it on, wait for it to boot (or resume), make the connection to the GPS receiver (oh yeah, where are you going to place the receiver so it gets a good view of the sky and also easily connects with the laptop?), load and run the navigation software and get it to see the GPS receiver signal so that it's all ready to use.
Think about the user interface of most PC-based navigation programs. They are mostly keyboard based. This is great when you are immobile at a desk. It's not so hot in a moving vehicle. The ones that support a touchscreen interface require a touchscreen. Most programs don't support them. Most laptops aren't equipped with them.
Many of the PC-based programs really aren't personal navigation programs. They are trip planning programs that have had GPS reception and navigation functions grafted on. They work, but still have rough edges. So far I've tried MS Streets&Trips 2008, DeLorme Street Atlas 2008, Garmin Mobile PC and Garmin nroute on my Acer laptop. Only the Garmin programs do the nav functions as well as a personal navigation device. Only Garmin's Mobile PC provides an interface that would be useful in a moving automobile but it requires a touchscreen if you want to use that part of the interface. Otherwise you are still stuck with the keyboard.
On the other hand, you can purchase a very nice personal navigation device for a couple hundred bucks ($800 is w-a-y overkill unless you want a lot of stuff that has nothing to do with navigation). A personal navigation device will have a vehicle mount that will let you position it in exactly the right spot for you, without impinging on the passenger's space. The nav device will clip into the vehicle mount instantly and with one hand.
If you take just a little care in selecting your personal navigation device, it will be one that starts up, gets a satellite lock and is ready to use in seconds (typically a very small number of seconds). And it will have a touchscreen interface that will be quite easy to learn and use.
The bonus is that if you select the right personal navigation device you can also carry it with you in your pocket, ready to pull out and use even while walking or if you need to find the nearest restaurant, gas station or an address. It will be most useful in these situations because of the quickness of startup compared to a laptop.
I'm not knocking the use of laptop GPS programs in general. I'm just not satisfied that they are ready for primetime for quick and simple and versatile personal navigation. At least not yet.
In the interest of full disclosure, I own a Garmin iQue 3600 (Palm PDA with integrated GPS) that I have been using for five years and is still my favorite for navigation, a Garmin eTrex Legend HCx and a variety of PC laptop programs; the ones mentioned above plus I'm about to try out the latest iGuidance program from iNav, Mappoint 2009 and Streets&Trips 2009. I do this as a hobby/personal interest and I have no affiliation of any sort with any company.