As of February 21 ,2008 ,The Sharper Image is no longer accepting gift certificates or gift cards either in the stores or online. Do Not Buy These on Ebay ! You will become a creditor in the company's bankruptcy and will likely never be able to redeem them.
There is a blog that calls itself the consumerist (google it) that will give you the scoop. Here's a chance to avoid an Ebay ripoff. Stay away !