IDG News details the challenges IBM has faced in ramping up 90nm processor production in their East Fishkill plant. The poor yields were cited by Apple as the reason for the shipping delays on the Xserve G5 last quarter.
The rest of the industry has also seen delays in 90nm Production. AMD is expected to reach commercial production of 90nm chips late this year ("September-October-November"), while Intel appears to be in production at this time.
Apple's new PowerMac G5 updates will likely use the 90nm part from IBM. Readers finally report shipments of their Xserve G5s, indicating that production is proceeding. PowerMac and "metallic" display updates are still expected shortly.