Thanks, Asif. Not much here, but it's better than nothing.
I'm pretty sure helicopters are
confirmed though. Absolutely no air travel would eliminate the player's free roaming capabilities and wouldn't be able to explore the "new" Liberty City more in depth/quickly.
Edit: According to his blog..
GTA IV super exclusive preview next month on 14th June 2007
Looks like we're about a month away from some big details!