Having an Options panel is definitely not crucial to the success of a WordPress theme, but it will help your theme to appeal to a lot of additional users. If you are a theme designer, you may have wondered whether it is difficult or not and how exactly to set this up. It actually involves the creation/altering of four files: functions.php, header.php, style.php, style.css. If you’d like to set this up for one of your themes, The Undersigned has made a great post detailed how to add options to your WordPress theme, where you are walked through the steps it takes to add an options panel. I recommend giving it a shot if you offer a WordPress theme. It could help double the number of users.