So, which of these places must we stop at?

"It's the statue, man, The Statue."

That's why the passengers have difficulties standing up in place : the line have been designed for confortable runs at 350km/h, they didn't smooth it for the 570 km/h run. The swoosh is on because of the very high speed, and the fact that it's a fairly new line ; most of that dust isn't risen at normal operating speed. And the cars are climatized, but there is no need for pressurization...

The lines are indeed dedicated, and no cows wander on TGV lines (for their own safety ; at that speed the cow won't survive (the result would make Happy tree friends seems nice) but the train will). And they are built for 350 km/h ; service starts in a couple months.

Un roi sans divertissement est un homme plein de misères

Trains have to fit within strict ride characteristics criteria at a speed of maximum service speed +10%. For these trains, that would be 352 km/h. 574.8 km/h is WELL above that. Also consider that the main force acting, aerodynamic drag, rises with the square of speed, e.g. during the record it was more than three times of what it will be in normal service.

Are the lines dedicated

Yes, of course! Like Madrid-Sevilla/-Toledo or Madrid-Lleida. They have to have curves of only large radiuses (otherwise tracks would have to have large inclinations and passengers would feel strong forces), the two tracks of the line must be at a larger distance for safe passing, rails must be strong enough and switches shouldn't be bumpy, the catenary must be very tense, no slow trains should get in the way, there should be no level crossings with road, the signalling system is special, and various safety measures should prevent f.e. a cow coming on the line.

Are the cars pressurized like a plane?

Yes, to some extent. Going fast (=>pressure drop) already calls for it, and high-speed trains going across tunnels have to 'filter out' the pressure shocks at the portals, or else passengers' ears will pop.

What happens to the nearby land with the regular swoosh?  The dust cloud behind it.

At regular service speed, the right-of-way is enough, and there is no dust cloud. You can stand at the foot of a catenary mast and watch a train go by (though there it would be a bit loud and you'd feel strong winds). Interestingly, if you go to the www.record2007.com homepage, go to the history section and watch the videos of the earlier French records, you'll see that the 1955 record runs looked just like the present one (pantograph pulls arc-lights, dust cloud, bumpy ride), while achieving a record (331 km/h) around what is normal service speed now.

what are the reasons to beat more records

Publicity, what else. Hope for new customers from across the pond (including South America), and leaving a greater impression than rivals. Hope for more willingness from the French state to order more trains. Hope that some people who had no clue about the new TGV Est line and would have continued flying/driving now took notice. Plus, a little bit of worthwile research, trying to find eventual problems that show up faster at a higher speed.

instead of choosing, say, 300-350km/h

These trains are for that speed range, this line will go in service with 320 km/h. The record run was one-off, and I guess it cost much less than a new line.

_{*Lunatic*, n.
One whose delusions are out of fashion.}

• A back-of-the-envelope calculation of mine about the power use of a high-speed train and an A340.
  
• A later follow-up, with comparable numbers calculated for litres of fuel per passenger-kilometre, assuming electricity for trains from petrol-burning power plants.
  
• Afew's Air Fare Blair diary.
  
• A discussion on cars vs. trains with focus on consumption.

• Freight transport: train 29, river barges 35, road (lorries >3.5t) 96, airplanes 665
  
• Local passenger: buses 77, trains 98, average private car 148
  
• long-distance passenger (includes high-speed ICE): buses 33, trains 52, average car 147, [domestic] planes 183

Congratulations to everyone who made it happen.  Genius and hard work go unrecognized FAR too often.  Anyone who has ever tried to do something difficult stands in awe of your accomplishments.

"Remember the I35W bridge--who needs terrorists when there are Republicans"

Glory is underestimated, though feeding the poor is not bad either.

Peak oil is not an energy crisis. It is a liquid fuel crisis.

Don't write them off too fast: an extension of the Shanghai line to Hangzhou is still in the plans (for 2010), and that's 170 km, enough for a very nice record. (They achieved 501 km/h on the just 30 km long present line.)

Regarding the catenary critical speed, how do you imagine a double catenary with different mechanical tension? If you mean side-by-side, then both will have their own critical speeds, nothing solved. If you mean fastened to each other, that doesn't work, because the catenaries move in every direction: say if there is a temperature change, and one catenary lengthens more than the other, the tension will be transplanted.

_{*Lunatic*, n.
One whose delusions are out of fashion.}