MacBidouille posts some unconfirmed (new source) rumors regarding Xserve updates.
They claim the Xserve will be upgraded to the G5 around September, and maintain that the PowerBook G5's will not be available before 2004 due to heat issues. Further notes claim that the Power5 is due in December, with PPC 980 chips arriving in 2004.
MacRumors readers have speculated about an Xserve update after the introduction of the new PowerMac G5's... and it does appear that Apple is offering Developers deep discounts on current Xserve and Xserve RAID units through July 31, 2003 -- causing some to speculate that they are attempting to clear out these items. No other evidence is yet available on these updates.