No longer will you be limited to inviting your mates round for a good thrashing round the tracks of Gran Turismo.From gamesradar:
confirmed that the current plan is for GT4 to include full network support. This would allow gamers to race head-to-head online, via broadband networks (which are due to launch in Japan and the US later this year, although a UK launch date has yet to be announced).
You can connect to a track to race against people with names like "1337Rac3r" and "NismoDooD"