Looks like we'll have to wait until June for our first glimpse.
It looks certain now that we won't get to see San Andreas at this year's E3. SPOnG.com is reporting that, through a conversation with Take Two, that there will definately be no GTA love at the exhibition.
We'll know for certain in a few days, when Take Two officially release their E3 lineup. But unless this is a big PR stunt, we'll only have to wait till June: where the game will be "unveiled [...] to selected press, retail and distribution partners."