Update - The release notes are now available here:  https://na1.salesforce.com/help/doc/en/salesforce_spring13_release_notes.pdf

The salesforce.com Spring ‘13 release is quickly approaching and soon you'll be able to take advantage of exciting new features and functionality! If you are a Force.com Sandbox customer, you have the opportunity to get early access to Spring ‘13 in your Sandbox and test new customizations and features before your production organization is upgraded.

The Sandbox Preview window for Spring ‘13 is scheduled to begin January 11, 2013. If you would like your Sandbox organization to take part in the Spring ’13 Preview, your Sandbox must be active on a preview instance by January 11th , 2013 to take part in an overall instance upgrade.

Please read carefully and follow the instructions in the next section for specific information on how to handle each of your sandboxes.  In a lot of cases, you will not need to do anything, but you may need to take action by January 4, 2013 in order for your sandbox to take part in the Spring ’13 Preview.

What Do I Need to Do?

General Information about Sandbox Refresh: From now until January 4, 2013, all sandbox refresh requests will be routed to an instance that will be upgraded for the preview.  Starting January 5, 2013, all refresh requests will be routed to non-preview instances.  We will continue to route refresh requests to non-preview instances until all production instances are upgraded.

Plan for the Preview: You have from now until January 4, 2013 to decide if you would like your Sandbox to take part in the Spring ‘13 Preview. Follow the steps below for each Sandbox org that you have.

Note: If you have a full Sandbox, be mindful of the 29-day refresh policy and plan accordingly. 

1) Determine your Sandbox instance: To determine which server your Sandbox is on, log into your production org and navigate to your Sandbox List page (Setup > Data Management > Sandbox).

Determine your sandbox instance by using the location column above.

2) Refresh?…or…Don’t Refresh?...or… Do Nothing – You have options!  Once you have located your instance, use the chart below to determine if, when, and what action you should take on your Sandbox.

Important: 

• The January 4, 2013 deadline is to ensure that all requested refreshes are complete by January 11, 2013. If you have a large Sandbox, please keep in mind how much time it takes to complete your Sandbox refresh to ensure your copy is completed by January 11, 2013. This may mean that you need to request your refresh in advance of the January 4, 2013 deadline to ensure it completes by January 11, 2013.
• If you are refreshing onto a preview instance, DO NOT refresh after you activate the sandbox on your preview instance.  If you do, you will be refreshed to a NON PREVIEW instance.
• If you decide to stay on the current Winter ‘13 release, your Sandbox will not be upgraded to Spring ‘13 until February 9, 2013.

AppExchange Preview Instructions

Additional Resources:

Sandbox Preview FAQ

Understanding the Preview Window Refresh Schedule:

In addition to the steps above, use the following graphic to understand what will happen to your sandbox.  For example, if your sandbox is on CS12 and you refresh it after 12 AM PST on January 5th, it will be moved to a Non-Preview Instance.

If you have additional questions about your Sandbox options in conjunction with the Spring ‘13 release, please contact salesforce.com Customer Support.