The sign-up doesn't take long at all as they don't even ask for your console information on the initial sign-up this time around; just a few simple questions and you'll be well on your way to getting in. All the information you need can be found on Major Nelson's blog.
Before you sign your life away and agree to Microsoft's Terms of Service, there is a little disclaimer that can be found tucked away between the finer points of the agreement. It reads a little something like this:
You acknowledge that due to the unique nature of pre-release software update programs, there is a risk that this software update may impair your console’s functionality or even render it inoperable.
Is getting the new dashboard a bit early really worth the slight chance that your Xbox might become a very expensive paperweight should you sign on the dotted line and agree to Microsoft's terms?
Xbox LIVE Preview Program [Major Nelson]
can cause it. You can fix it by adding *.disqus.com to your whitelists.