[caption id="attachment_85" align="alignright" width="150" caption="Gift card"]
We just finished building our new Gift Certificate component for CommerceCM and spent a lot of time researching the issue of expiry dates.
In most jurisdictions in North America, the sort of pre paid purchase cards or gift certificates you would buy online cannot have an expiry date. Common exceptions are promotional cards (Spend $50 get a $10 gift card), cards used for charitable purposes, or cards used for a specific product or service.
For US regulations, check out the Consumers Union Site
In Canada, most regulations seem to have been updated November 2008. Here are some resources from either end of the country.
While I am not familiar with any case law, I assume that online merchants should adhere to the regulations in the jurisdiction they are based or have a physical presence (like sales taxes). In practice, I always recommend that they follow the most restrictive definitions to avoid trouble.