When should I start using WCAG 2.0?

Very nicely done FAQs in my opinion, especially this one:

When should I start using WCAG 2.0?
WCAG 1.0 is the stable and referenceable version. A complete Working Draft 
of WCAG 2.0 is available, yet some aspects of it are changing based on 
comments received. Some people may choose to wait to start using WCAG 2.0 
until the documents are more stable, and additional views and supporting 
material are available.
Some organizations have already started using WCAG 2.0. There are many 
benefits to using WCAG 2.0 Working Drafts in your current and upcoming 
projects:
WCAG 2.0 is more applicable to current technologies, future technologies, 
and non-W3C technologies. 
WCAG 2.0 supporting documents, such as Understanding WCAG 2.0, provide 
more information to help you understand and implement the guidelines.  
You can develop and submit techniques that may be added to Techniques for 
WCAG 2.0. 
You will be ahead of some others, and when WCAG 2.0 is finalized, you will 
be able to meet it sooner. 
If your site is required to meet WCAG 1.0, you may choose to develop it to 
meet both WCAG 1.0 and WCAG 2.0.
After reading the Overview of WCAG 2.0 Documents, the best place to start 
using WCAG 2.0 is the Quick Reference.

a WCAG 2 FAQ at:
  http://www.w3.org/WAI/WCAG20/wcag2faq.html

Regards,
Phill Jenkins
IBM Worldwide Accessibility Center
http://www.ibm.com/able