Don't know if anyone else has seen tonight's gadget show broadcast in the UK where an incar computer was tested. XP based with voice recognition it featured satnav, Office 2007, DVD video and music playback, VOIP and phone control. It was also able to connect to the tinternet via wifi and 3G.
Here's a link with photos http://gadgetshow.five.tv/jsp/5gsmain.jsp?lnk=401&section=Features&show=s9e2&fea tureid=813&description=In%20Car%20PC

However with the exception of voice recognition, and native Office 2007, I was hard pressed to see where it scored over a tablet.

For video and music we have Canola2 v(others are available). Satnav we have wayfinder (steady, I quite like it anyway)and Maemo mapper. We have Voip, and phonelink for the phone control, if you don't have a nokia smartphone(! for which nokia should port some of the labs apps).

The featured 'puter also had 160GB of storage which beats the 32Gb on my N800, but I could connect via USB to an external HD of my choice.

The article showed Jason phoning his local coffee shop to get the guy to bring him a coffee, checking his google mail, opening an attachment in Word 2007, and then composing a reply using speech recognition, that bit was very cool I must add. He also ordered a pizza, and navigated to the local supermarket.

virtually all of which I could do with my N800, bluetooth keyboard and GPS, and my kit goes in my pocket!

Like all these things, sometimes people get carried away with stuff.
I can honestly say that never in my life (and I am in my 40s) have I had a need to use any version of office for anything in my car!
Having said that, from the front seat, I don't want DVD video either (I could possibly want the news if I was waiting for someone I guess).
I want a decent GPS, and arguments aside, the IT doesn't have that currently (something as usable as say a tomtom) from my POV.
I want music, and to me 32GB is enough. It doesn't have to be encoded at huge quality, you are in a car.
I don't really see VOIP as useful in a car, although phone control is handy. Not so sure about the abilities of speech recognition. If I get phoned by someone in a car sometimes I can't tell what they are saying, what chance does the computer have.
I never want to order a pizza in the car. Ever.

However, I do want the things that I would consider a car computer useful for, which you haven't mentioned. I expect it to store the radio traffic reports in case I want to listen to them at some point. I want it to alert me if there is traffic the way I am going (I guess the tomtom replacement does that). I want it to tell me how much fuel I have, and where the petrol stations are along the way. I want it to tell me what my fuel economy, range, average stats for driving.
I want it to tell me that I need to put some washer fluid in the car next time I can, or that the wheel bearing on one side of the car is over hot.

I also expect (and this will become reality at some point soon) it to slam the brakes on if I am so busy playing with the electronics that I haven't noticed the car in front of me stopped.

Maybe it would be handy if when wobbling around lining up to overtake it gives me a percentage chance of succeeding :-)

Then when I get where I am going and there is a little space, I expect it to analyze the space, tell me if it can fit in it, and either guide me in or do it for me.

Now that is a car computer. What you described is a PC put in a car for a laugh!

Oh I agree absolutely with most of your points.

I like wayfinder as I now have one bit of kit which is portable. I appreciate TT etc now do Mp3 playback, but I cannot telnet or VNC into my myth box at home.

Like you I would never dream of needing to load office in my car, but I can see some who would to read attachments.

I also use carman, which is really not much more than a toy but does show some interesting data.

What I would really like to see are

a link between carman, GPS and the internet so that a database of fuel stations and prices in say a 15 mile range along the route can be downloaded and displayed on the satnav with a choice of detours to either the nearest or the cheapest when the fuel reached a certain level - say a 1/4 tank.

You can already traffic radio service available over the internet from the UK highways agency. I've had a listen and for me ( with a near 40 mile commute) the area covered is too large, to similar to listening to national BBC. Be good if it was possible to download a podcast at regualr intervals. Wayfinder already has traffic info alerts, which are mixed in my area probably as the road network is not as monitored as busier areas.

Rather than full blown voice, simple voice tags for commands would be extremly useful, such as play, pause, next etc. Similar to the voice controlled dialing most phones have.

I have mobile broadband on my phone, so any internet based stuff is already possible. I have once used it to download a menu from may favorite indian takeaway so we could choose, and then phone an order to collect on the way home.

A lot of this stuff is there already, but the bits just need putting together correctly.

I find wayfinder rather underwhelming, but that may be because tomtom is rather good.
I would point out that it is probably not a good idea using telnet in a moving vehicle!

Depends. i would want either it to know when fuel was at the last 60 miles or so, or when there was a tanker strike, or if it was christmas day or something. Really I would like it displayed, but no detours unless I asked.

Again, having used mobile phones, and having an iPod in the car, I really prefer the next/previous buttons on my car steering wheel. I can talk to my passenger without the computer interfering, and change the volume/track etc.

Well, yes, I use the internet on the phone too, although if you are travelling it gets really patchy if you need a constant connection.
Certainly nothing you want to rely on.