My best guesses...
The following are my best guesses for PM G5 updates. Please note that these guesses are based on speculation only, and I have no insider info.
Date: March 30/04 (after the U.S. memory rebates to clear out old stock end, but prior to IBM's Power roadmap announcements - Steve hates to be upstaged)
Processor: 90 nm 970FX (smaller and less expensive to make)
Processor speeds: dual 2.0 (keeping the same motherboard as the current top end model), dual 2.3 (remember the xServe graphic?), dual 2.6 (wasn't there speculation that IBM was already producing 2.4 GHz chips?)
Bus speeds: 1/2 of processor speeds
Optical drives: combo drive in base model, 8x SuperDrive in other 2 models
RAM: 256 MB in base model, 512 MB in other 2 models (this is Apple, after all)
Price: $2199 (sorry, upgrades to dual processor and PCI-X motherboard), 2599, 2999
Also, dual 2.3 xServes will be announced (in addition to the dual 2.0's).
I expect single 1.6 and 1.8 GHz G5 iMacs will be announced this summer, possibly in the same brushed aluminum and (this is wild speculation) featuring detachable 17, 20 and 23" Cinema Displays (if they could use the same manufacturing process for these as their other Cinema Displays, it would save them $$$).
I'm so confident in these predictions (NOT!) that I'll eat my left hand (apologies to NeatGekko) if ANY of them are right!