The New York Times reports that the PowerMac G5s are due to arrive in stores on Monday (August 18th).
This expectation is confirmed by numerous word-of-mouth reports that also claim the G5s will make their public appearance this week.
Reportedly, Apple already has 100,000 pre-orders for the PowerMac G5. Users have been waiting the the shipment of the new machines, after Apple introduced them in late June at the World Wide Developer's Conference.
Adobe will also be releasing their Photoshop Plug-in for the PowerMac G5 on Tuesday, which improves Photoshop performance "75 to 200 percent".
Update: Our own reports indicate that PowerMacs were shipped out to stores on Saturday and are expected at most stores by mid-week. Stores will have limited supplies.
Apple.com now reflects that PowerMac G5s are Now Shipping. Press Release notes that the 1.6 and 1.8GHz PowerMacs are shipping, duals later this month.