IGN Speculates that the 360's GTA IV Second User Content to debut 6-1-09.

[JaggedSac]

Here are my MS E3 conference thoughts.

Lionhead game reveal.
2 Rare retail game reveals.(KI and PD)
Perfect Dark on XBLA reveal.
BigGames(recently aquired studio) game reveal.
EPIC game reveal.
ODST gameplay reveal.
Motion detecting device reveal.
New NXE features reveal.
More Primetime games reveal.
Zune\Live integration reveal.
Crackdown reveal.
ZuneHD gaming capabilities reveal.
GTA DLC reveal.
They will go over sales numbers.
XNA feature additions. Maybe motion controller API additions.
Avatar customization kit reveal.
Maybe a 360 redesign.
That is all I can think of for now.