is to use the course creator to re-create my route home from work and take the car I drive to work everyday and see how quickly I can possibly get home after work!  
    
its not far, only a few miles.  
the plan is to use my phone to record the topography and altitude of the route.  
 
In real life I can get home in less than twenty min on a good day. I bet I can do it in less than 5 flat out!(in my same car.) 
 
Now that the track editor is a real thing I am actually going to start taking this seriously!  

There's something seriously wrong with you if you want to spend your game time driving home from work.

Did you dream it was coming out?
 
 
Badumtsh.

Did you dream GT5 was great, I saw it at gamescom yesterday (blogged about it) and I gotta say that I am not impressed by the game. 
 
edit: though I like your idea :-D

"There's something seriously wrong with you if you want to spend your game time driving home from work. "

They should have a cross country driving mode. REAL TIME BABY! YEooWW!!!

That's actually a pretty rad idea.

Track editor? WOW that's cool!

I want to put a bitchin' fire bird on the hood of my Chevrolet.

Awesome idea dude

The Course Maker is more like a Course Generator, it's no Modnation Racers. Here's a run down of it from 1up.com:

Yamauchi then points out that GT5 has a Course Maker, not a course editor. He initially wanted to offer a tool that would allow players to create everything from scratch, but that would require producing a crazy-intensive CG tool that would intimidate players too much. So he opted for a system that would allow pretty much anyone to make a cool track.

The idea is that after selecting a theme (such as "early evening in Toscana" or "Germany in spring"), you'd then tell it to tweak some parameters (such as number of sections, one-way versus looped courses, weather, and time), and tell it to crunch those factors into a randomly generated map. Yamauchi likes the fact that "each course generated will be a genuine surprise" through this system. Of course, you can also share courses and race online with buddies in your creation.

Yamauchi demonstrates the Course Maker by selecting a Toscana theme and making it a one-way course with four sections. He does stuff like fiddle with the numbers for the frequency of curves, the sharpness of corners, and even the degree of topography. It's super fast and easy to tweak these numbers and then go right into a test drive before sharing the track with buddies -- and he demonstrated how fast the game can just create random and varied courses even when crunching the same numbers and parameters.

Game isn't coming out.

" Did you dream it was coming out?   Badumtsh. "

Still I think its going to be a speed tree like course creator.