FWIW - I've started my project in ernest.

I bought a Samsung 840 SSD (120G) and got Windows 7 optimized to to take advantage of it. Boot, sleep and wake times are absolutely amazing. I'm getting some confidence that a car PC will be practical for day to day use.

After a lot of research and a few trial installations of front-end software, I ended up purchasing Cenrafuse. I'm still in the process of configuring it and deciding what plug-ins I want. I got the nav package with it, but without a GPS reciever, can't say much about it's functionality. My initial impressions on the nav are "meh".

Right now I'm temporarily setting up data and media on a regular 3.5" HDD (1 TB). Once this is set up, I'll buy a 2.5" HDD and copy the data over.

When I get some more time, I'll probably set up a seperate build thread. This project will likely take many months to plan, buy and install, but I'm starting to get excited now.