Had an idea about how *we* and Polyphony Digital might be able to get Prologue style online leaderboards into GT5.
I don't think the issue is with managing the basic car + track + time info, but saving / loading and storing ghost laps for 1000's of cars & circuits would prove extensive and would certainly push GT5 server bandwidth.
My little idea here would be to offer to host ghosts ourselves in the various communities of the internet. Where ghost data is present the game (via the user's PS3) can load it, where it isn't, at least there'd be a best lap time... At the very least, small communities / friends would be able to share and race against each other's ghosts.
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here.