UPDATE: many people are complaining about poor VoIP quality on the Nexus One. My experience is that the Droid handles VoIP much better. See comments below for more info.

I just got my Nexus One today and the first thing I did was set it up for VoIP calling. I'm using it on a T-Mobile data-only plan (no voice minutes needed).

This tutorial assumes you will be using Gizmo. To use Gizmo, you'll need an existing account.
If you don't have a Gizmo account, use an alternative SIP provider. There are a lot of options.

Evan Charlton said,

Also, if I decide to discontinue support for the GV project, it's open-source software under the Apache 2.0 license, so feel free to fork it to your heart's content.

This tutorial assumes you will be using Gizmo. To use Gizmo, you'll need an existing account.
If you don't have a Gizmo account, use an alternative SIP provider or purchase a Gizmo account on eBay. There are a lot of options, but I think Gizmo is the best. The last account I bought on eBay cost $5.

See this link for some alternatives if you don't have and don't want to buy an account Gizmo:  http://www.google.com/support/forum/p/voice/thread?tid=4fceba98c89deaed&hl=en

This is a nice initiative:

Canonical aims to improve the Ubuntu user experience by fixing a multitude of minor usability glitches. The project, which is called One Hundred Paper Cuts, will entail a collaborative effort by Canonical's new design team and the Ubuntu community to fix one hundred usability bugs before the release of Ubuntu 9.10.

Read more:

http://arstechnica.com/open-source/news/2009/06/canonical-to-boost-ubunt...

http://blog.davebsd.com/2009/06/10/one-hundred-paper-cuts/

R. McDougall over at climbing-the-hill.blogspot.com was motivated recently to mock the "Linux is not ready for the desktop" articles that are written by people who he feels are "carrying around the self-serving assumption that their preferred OS embodies the only real way to organize a software ecosystem." See his "Why Windows Is Not Ready For The Desktop" post.
 
And to counter the arguments that Linux is irrelevant on the desktop, see  Carla Schroder's post "1% Linux Market Share = 100% Dishonesty". Carla says, "If Linux is such a pipsqueak, why are there such relentless tides of propaganda and deception against it?"
She also references Matt Asay's article,

Keith Curtis worked at Microsoft for 11 years, coding on Windows, Office, and at Microsoft's research department, before leaving the Redmond giant. Call it a revelation, call it giving in to the devil's temptations, but he's now a complete open source and Linux advocate, and in his new book, "After the Software Wars", he explains why open source will prevail against Microsoft's proprietary model.

Curtis never actually used Linux until 2004, when he left Microsoft. Over the years, he turned into a Linux advocate, and now claims that thanks to the proprietary software model, we are living in "the dark ages of computing." This is what is scientifically known as doing a complete 180 (no, not a 360).