zeppelincheetah at PlanetGrandTheftAuto.com points out a pattern of teaser sites launching on the first of July.
July 1st, 2001 - The Liberty Tree - Rockstar's initial teaser site for GTA III.
July 1st, 2002 - Kent Paul's Nostalgia Zone - Rockstar's teaser site for Vice City.
July 1st, 2004 - ??? - Rockstar's teaser site for San Andreas.
Let's hope something happens on July 1st.