Since version 1.1.1 it is possible to assign conditions to gift certificates. Those conditions are added and processed in similar fashion as Shopping Cart Rules conditions. To use this feature you have to enable it in global configuration settings.
On the page you will see a widget that allows admin to set various conditions which have to be valid for the cart when certificate is applied for it to be accepted.
Configuring conditions is the same as configuring Shopping Cart Rules conditions.
For any product attributes to be available in conditions they have to have 'Use for Promo Rule Conditions' set to 'Yes'
You can also limit certifcate usage to selected store.
For this setting to have an effect, you must have this setting enabled.