According to the most recent anonymous reports... Apple is planning on introducing both 1U (single G5) Xserves as well as 3U (dual G5) Xserves at MacWorld Expo. No knowledge processor speeds are available.
These two sizes would be a bit unusual from a space/power standpoint, in that two 1U machines would provide more power and less space than a single Dual 3U machine.
Regardless, ongoing hints have suggested that Apple has been working on both 3U and 1U enclosures for the Xserve.
Update: A new higher capacity Xserve RAID was also mentioned in the same a reports.
Related Forum: Mac OS X Server, Xserve, and Networking
