How easy will it be for you to switch WordPress themes in the future? Most theme users probably don’t ask themselves this question. Why would you? WordPress lets you switch themes with a few clicks so things should work smoothly. But that’s only the case if your theme was developed following WordPress standards in order to avoid the lock-in effect.
Much has been written for WordPress theme developers in the last couple years on the lock-in effect while hardly anything has been aimed at theme users like you to explain what the lock-in effect is and how to avoid it. I feel this is necessary because there are still many themes built without consideration for your ability to switch in the future.