There was support for Sun's SPARC systems with Ubuntu 6.06 but then in 2008 the official Ubuntu SPARC support was dropped. The SPARC builds continued to be produced, but Canonical would not be providing official builds from Ubuntu 8.04 LTS onwards for this Sun architecture. Two years later, the state of the Ubuntu SPARC support continues to decline and is reaching a point where Ubuntu's technical board feels it no longer should even exist.
Canonical's Scott James Remnant has announced, "The Ubuntu SPARC port has been declining in both levels of usage and maintenance, and its quality has now fallen below the minimum level we expect to be an Ubuntu port. After discussion at the recent Ubuntu Developer Summit, and ratified by the Ubuntu Technical Board, a decision was taken to decommission this port at the Feature Freeze point of Ubuntu 10.10's development later this year." The Ubuntu IA64 port right now is in a better state than SPARC, but Scott went on to share that it will be sharing the same fate as SPARC.
This announcement is being shared now though as a warning shot and in hopes that any Ubuntu SPARC/IA64 stakeholders will step-up and takeover the maintenance work so that these ports will not need to be decommissioned. However, in order for this to succeed, significant work would need to be carried out on the tool-chain and kernel especially, among other areas.
Ubuntu 10.10 will likely not see the light of day on Sun SPARC and IA64 Itanium systems.