It doesn't look like it's much of anything.
New firmware 2.17 is up for all PS3 users (description: "the operating stability of some online PS3 titles has been improved.") - and there is hint it's needed fot playing GT5(thanx Tiduz from Neogaf):
Tiduz"Please install firmware 2.17 on your PLAYSTATION 3 which is available from the 13th of March. Before playing Gran Turismo 5 Prologue™, please make sure that this firmware has been installed on your PLAYSTATION 3."
from gt5 beta test, wont say who i got it from. Up to you to believe me or not.
Intresting.
From the Prologue thread:
I, nor anyone else, seems to have any idea what was included, but the update is there. I checked Google, the Playstation forums and the Playstation blog -- nothing of interest.
Anyhow, get it while it's hot.
If you had searched you wouldn't have needed to start a new thread!
There is a perfectly good and rather large system update thread which you can't have missed!
Please don't start threads like this until you have searched first...
https://www.gtplanet.net/forum/showthread.php?t=89449&page=19