JUNE EDIT: ROCKSTAR GAMES ARE NOT AT E3 - GTAV WILL NOT BE THERE
Everything below is from back in April. Rockstar did not attend...
Okay here's the e-mail I received from Rockstar Support on 05 April 2012 16:01:25
Jared H, Apr 05 11:01 am (EDT): Hey there,
Thank you for contacting R* Games Support.
At the moment we don't have any more information regarding GTA V aside from what has already been released in the press. I can't confirm or deny that the main protagonist of GTA V is in the trailer, you'll need to wait for our future announcements. I know it sucks waiting on info, I'm curious to know myself.
The newswire and twitter are going to be the best sources of information regarding GTA V. Also, PAX East is happening this weekend in Boston so some information may be coming. We're also fairly close to E3.
Wish I had some better news for you. Hope you have a good day.