I've just finished watching the Giant Bomb quick view of GT5.  First of all despite being more of a 360 man at the moment, I've always been a fan of GT games, I had 1 nd 2 on PS1 and 3 on PS2.  Forza 3 is what filled that gap and filled it very nicely I might add.  I never liked the lack of visual damage in GT games.  I watched the whole video, am I going to rush out and buy a PS3 just so I can play it?  In short - no, there was a time when I thought I might, and you could argue GT5 is a more complete game than Forza 3 - you'd probably be right. 
 
What I get from the video though, certainly in comparison to Forza, is that the visuals aren't actually all that amazing, as I understand it a lot of the car list is actually multiple models - as you got with earlier GT games... And the driving dynamics are fine - but nowadays they are fine in many, many games.  So what does GT5 have going for it?  It wants you to think it's the best game since sliced bread and opens up a new era in driving games.  Personally I don't think it will do that.  It seems fine, like an competant driving game, what it does seem to have is a great deal of choice, and in that some things you might argue Forza is missing.  Driving dirt, snow, ice, night time, weather - these are all something it has over Forza.  If both games were on the 360 I guess I'd be tempted - but I wouldn't buy the console for it. 
 
How about the Dunsfold aerodrome Top Gear test track?  Well, that would be nice - I'd love to compare times with the Stig, but I can see a major issue with this.  This will be a very clear indicator of how realistic the claimed 'realistic' driving simulator is.  Let's say we've got half a million people playing GT5 in the Uk, racing against the Stig, you should find that the lap records for different cars match the power laps board.  If it ends up grossly out - then that will indicate that actually the driving dynamics of the cars probably aren't accurate.... 
 
Of course it will be interesting to see how this pans out - maybe I'll be proven wrong and GT5 will be proven beyond a doubt to be the ultimate realistic Driving simulator?  We'll have to wait and see.