The Nexus One gets some hacker love from a certain "Max" of NexusOneHacks.net, who's figured out a way to install Ubuntu on Google's smartphone—without removing the Android installation. This means those who can pull off the install can still use their rooted Android OS mobile normally, launching Ubuntu as a sub-system when needed.
Why would anyone bother running a desktop OS on their smartphone? Max lists a couple of scenarios:
"I... see many... engineering [students] when they are studying Ubuntu/linux. Instead of heading to the lab or having dual-boot on their computer, students will be able to use their Nexus One/Android phone as a test device."
"[F]or web designers, their Android phone can become a portable test web server to test out their new designs."
And of course, the prospect of running desktop Linux software on a phone is awesome. The full step-by-step is here. Needless to say, the procedure—which requires rooting your Nexus One or Android smartphone—may void the warranty. A video walkthrough is also available below: