Would anyone like to add their own comments that I can pass onto them?
Well, I don't often have opinions ... ... but since you asked ...
I use both.
Personal Navigation Devices (PNDs) can be mounted easily and safely in any vehicle, regardless of size and number of passengers. It simply isn't possible for me to safely mount a laptop or netbook in my Honda CR-V and still have easy access to all the controls. And continue my 39 year marriage to my navigator.
I used to use a Garmin iQue 3600. I have since replaced it with a Garmin Nuvi 765T. The Nuvi is superb for Point A to Point B city driving. I have the widescreen version so it is also pretty good for giving you some sense of what is surrounding you. It's far from perfect in that regard, but it's not bad. And a fair tradeoff for being able to easily and safely mount it in my car. (Life is just a never-ending series of tradeoffs, after all.)
The Nuvi 765T is also fine for using multipoint routes that I set up with Mapsource on my PC and transfer to the Nuvi. I can create them on the 765T by adding Via points into a route and it works in a pinch but it's a bit of a nuisance.
When buying a PND, one must be vigilant to be sure and get one with all the features they need. I can't speak about TomTom devices. Garmin devices come with many different combinations of features. Some Nuvis will not allow saved routes and will not allow Via points to be added to a route (e.g. Point A to Point B is all they will do). Some Nuvi models will allow Via points to be added to a route but won't allow saved routes. Some will only allow one saved route. Some will allow ten saved routes. ... You get the idea.
None of this matters for the people who just want to search for a nearby hotel or gas station or donut shop or Aunt Martha's address and get directions. But it matters a lot to those who want to plan trips in advance and save those plans on their navigation device.
In addition to routes, my Nuvi 765T allows me to save many waypoints (Favorites). I currently have over 200 entries in my Favorites on my Nuvi that I have gathered over the years I have been using a GPS for travelling. These are addresses of friends and relatives, hotels we like to stay at, restaurants we like to eat at, golf courses I like to play, gas bars that I prefer to use. They are scattered all over western Canada in places that we don't get to very often so it's handy to have a record of their location. I have assigned categories (Eat, Sleep, Shop, Gas, Golf, etc.) with appropriate symbols. Some even have multiple categories assigned (eg. a golf store appears whether I select the "Shop" or "Golf" categories).
I have also loaded a number of custom POI files to my Nuvi for hotel chains, golf courses, store chains, and a variety of attractions that may not appear in the builtin POIs that come with the maps. I presently have added about two thousand custom POIs to it.
My Favorites, the builtin POIs in the maps, and the custom POIs I have added can all contain addresses and phone numbers. My particular Nuvi model includes Bluetooth handsfree phone operation. So, I can select a Favorite, POI or custom POI and have the Nuvi use Bluetooth to dial my cell phone, say, to make a hotel reservation.
The handsfree phone functions on the Nuvi will also pull the complete contact list from the phone so I can use the Nuvi to search the phone's contact list and dial a number without ever having to take the phone from my pocket.
(As an aside, I bought the Nuvi 765T for not much more than the price of a decent Bluetooth handsfree device so, since I needed one of those anyway, I got the navigation functions almost for free.)
As part of my pre-trip planning I could have loaded geocoded pictures onto it for attractions we might wish to visit and used them as destinations to navigate to. I could also have loaded a bunch of tunes or audio books onto it and played them through the car stereo either using FM or connecting a cable from the headphone jack to the AUX input on the stereo. Whenever there is voice guidance from the navigation, the tunes are muted until the voice guidance is done.
A PND can be popped into its mount and be powered up and ready to use in a fraction of the time it takes a laptop/netbook to boot and load a navigation program.
If you occasionally need to navigate while walking, say, to get back to the hotel or from the hotel to a nearby attraction, many models of PND will allow battery operation and can fit into a pocket or purse when not being used in the vehicle.
As you can see, a good PND can be a very flexible and useful device. I just returned from a two week trip of over 4400km using my Nuvi 765T for both highway and city navigation. This also included some backroads travel using topo and trail maps. I used almost every feature it has. This was my first extended trip with it and I was mostly quite pleased.
I use Garmin's Mapsource and Google Earth on my PC at home for pretrip planning. When I'm on the road I use Mapsource on my laptop for in-trip planning. This gives me the big screen and additional planning functions that either don't exist on the PNDs or don't work very well on them. You would derive the same benefits from Streets&Trips (or Street Atlas) for those purposes.
If I was driving a motorhome or similar large vehicle with the space to safely mount a laptop or netbook or tablet I would most likely do things very differently. But that's not my reality. So I use the PND for navigation duties -- a PND that allows multiple complex routes to be transfered to it and stored on it -- and software on my laptop for the planning functions. Best of both worlds.
Clearly, some can't afford both or simply won't wish to mess with both and will have to make a choice. I know this is Laptop GPS World where the focus is on laptop navigation products but when helping someone make a decision like this I think it helps to provide honest personal experience about all of the alternatives. I hope nobody minds.
...ken...