After a 21 day evaluation period you must either purchase a license or remove the software from your computer. Alternatively you can use the free edition which is limited in functionality.
If you would like to purchase Silverlight Spy visit http://firstfloorsoftware.com/silverlightspy/purchase.
When you purchase Silverlight Spy you will receive a license key. Click the Enter license key button in the reminder window that appears when you start the evaluation version of the program and enter the key. Once the key is entered you will be able to use the purchased edition of Silverlight Spy without evaluation limitation and will no longer see the reminder window.
If you do not have the evaluation version installed, you need to download your copy of the software.
A commercial license is available to legal entities, including companies and organizations (both for profit and non-profit). The license allows for use by a single developer within that organization and can be transferred from one developer to another.
If you want to purchase a license, and you are the only person planning to use that license, then the Personal License is for you. Personal licenses are non-transferable.