I don't think it can substitute for a car GPS. The reasons:

1. The map is too small to see it in the car.
2. It needs full internet access when drive.

Both of these problems can eventually be fixed by third party or Nokia software. In the mean time, keep an actually useful GPS handy.

Speaking of the GPS, does anyone know how to lock the red dot of your location in the center of the map instead of having it move around while the map remains stationary?

I haven't been able to figure out how to do much of anything with it, but don't plan to waste much time on it. I've been using various handheld Garmin GPS for over fifteen years, used Street Atlas USA for a while around 12 to 14 years ago bfore I gave up on M$ OS completely. Lately, I also use TangoGPS and Maemo Mapper. All have different UI's that were quick to pick up on.

I'll just use other devices until Maemo Mapper is (officially) out for maemo 5.

To take of the screen being too small, they just need VOICE NAVIGATION with announcement of actual street names like Google Map Navigation. With actual announcement of street names, you dont' actually have to look at the phone that much while driving.

The GPS is standalone, by the way...

Then why this one needs internet connection? Just confused.

The internet connection is used for AGPS (basically a method to get a lock-on faster).

However, I believe there's a bug that makes the GPS useless without AGPS (even if you stand outside in the middle of a field all day long waiting for a signal) right now.

The GPS in my N900 works without AGPS, so if there is a bug out there it does not affect my device. I got a location widget on my desktop and it shows my location with and without data connection.

The mapping and routing software supplied with the device (Ovi maps) lacks a lot of functionality and the UI is bad. The maps themselves seem to be accurate, at least in the SF Bay Area.

I also hope for a substantial SW improvement, be it a better version of Ovi maps or a third party application.
My take: A dedicated GPS device is currentlly superior. The N900 with the supplied maps is better than nothing.

At first, I thought he was saying the screen is too small, but he said the maps are too small, which is different. I have used many GPS with smaller screen than the n900 and they all worked fine for use in a car.

It is just a matter of proper font and feature size. Voice announcement is certainly worthwhile, but not needed. Most of he GPS devices that I used could beep at best. I would prefer (clear) voice, but do not need it.