THIS POST IS OUT OF DATE.
I've completely rewritten the code behind Tagul cloud generator. The main purpose behind was to improve the way Tagul handle cloud shapes. Now the shapes should be more precise. Also new algorithms allow to use any kind of custom shapes for clouds. Here is a demonstration of Android shape:

Custom shapes are not available for Tagul site users yet because the front-end cloud building form must be enhanced to handle it. There is a big complaint related to the building form complexity for using. So I am planning to rebuild it to make it easier to build clouds and then add custom shapes support.

BTW custom shapes are ready to be used with the API.