Today I’m on an asking spree 😛
Anyhow… Right now I am developing a free WordPress theme. The problem is that I want to make it as flexible as possible so that is why I will use some theme options to set some CSS colors, widths and so on. My question is this:
If I assume that one of this themes will be used for a heavy traffic blog, how this will affect server performance? I will have an increase of SQL queries? Or something else (wrong) ?
I do not think there will be an increase in the number of SQL queries. Unless, of course, you decided to extend the worpress functionality by making the theme somewhat data driven.
However the size of your templates/images/CSS/javascript files may have some impact on the performance of the application.
As a general rule of thumb, if you are concerned about the performance of a web based app, it is always good to keep your files as light as possible.