Laguna Seca has been completely rebuilt and will return for GT5. Trial Mountain has also been confirmed.
“Gran Turismo Anywhere” will allow you to manage B-Spec races, right from your computer. You’ll be able to hold B-Spec races with your friends from anywhere in what are called “Remote Races”.
GT5 will feature a series of special events such as the Karting Experience, the AMG driving school, The Stig Challenge, Jeff Gordon NASCAR School, Sebastien Loeb Rally Challenge, and Gran Turismo Rally.
Point-to-point rally stages will be automatically and randomly generated – you’ll have to depend on your co-driver to give you the best instructions about the road ahead.
Rally mode can be played either on or offline.
Weather changes include temperature differences, air pressure changes, and humidity, affecting the surface conditions of the track dynamically.
Weather conditions are randomized. Forecasts for your race will be available but may not be entirely accurate, just like the real world.
Polyphony Digital has helped Red Bull Racing’s Adrian Newey design the X1 Concept – an “ultimate” racing car, free of any technical regulations.
Polyphony Digital has worked to improve engine sounds.
Yamauchi admits that, in certain situations – such as standing race starts in the rain with 15 other cars on the screen kicking up spray in front of you – the game may not be able to hold 60FPS. Otherwise, it will strive to hold 60FPS as often as possible.
The Volkswagen Kubelwagen, which has a drive system like the first beetle, and the amphibious Volkswagen Schwimmwagen will be in the game.
Many things didn’t make the cut in Gran Turismo 5, and work on Gran Turismo 6 has already begun.

A summary of what we know so far...

(perhaps put it in the OP ?)


cars
• 1000 cars (800+ Standard, 200+ Premium)
- new brands include Ferrari, Maserati, Bugatti, Lamborghini, McLaren, Tesla, Red Bull Racing
- new series include NASCAR, WRC, Super GT, karting

tracks
• more than 40 tracks (more than 100 layouts)
- new real circuits include Top Gear Test Track, Daytona, Indianapolis, Spa-Francorchamps, Nürburgring, Monza
- new fictional circuits in London, Rome, Madrid, Tuscany, the Alps, the High Fens

offline:
• single race, split screen, time trial
• license tests, championships
• A-spec & B-spec
• car tuning
• 8 MP photo mode
• GTTV (compatible with PSP)

online:
• up to 16 players in a race
• private rooms, lobbies with up to 32 players
• spectator mode
• text & voice chat
• photo- en replay album
• YouTube replay upload
• time trial rankings

other features:
• cockpit view for Premium cars
• damage & roll overs (all cars)
• day-night cycle
• dynamic weather
• track creator / editor
• skidmarks & reverse lights

tech:
• up to 1080p 60fps
• up to Dolby 7.1
• custom soundtracks
• PlayStation Eye headtracking
• 3DTV support (gameplay & 3D photo mode)

also:
• all cars bought in GTPSP can be transferred to GT5 for use in Arcade Mode
• Adrian Newey was involved in a way
• Sebastian Vettel did voice work

Rather than being a fully featured editor – a feature that, Yamauchi confessed, was tinkered with but deemed too complex – the course maker allows players to select certain set parameters to create a track. A theme can be selected, with the Belgian High Fens or Toscana two examples, and the individual track sectors are then defined.

Sectors are edited individually, with frequency of curves, sharpness of corners, degree of topography and banking angle are set with a series of sliders.

Yamauchi created one for the purpose of the demo, a 10km run through the Belgian High Fens. It was sparse but not without sparkle, with rolling hills and fields and the occasional environmental feature like a small village giving it the feeling of a long and winding country road.

GT5 Interview - Weather changes in realtime while racing; Driver's management is extremely important in this game; Endurance races also have this weather feature; A-Spec & B-Spec are both equivalent in this game but they're included separately in the game