I think the idea behind this is great; engaging and (hopefully) exciting your fanbase in a focused event is good PR.
What I'm concerned with is the proximity to E3...seems like it's too close to E3 to announce anything big as you would risk marginalizing your E3. Therefore I don't expect many big announcements, just more solid info on the games listed above.
Totally willing to be wrong though...I'd LOVE a Gears 3 announcement ASAP. Plus I have no idea what NATAL games we'll be shown.