How can I get a count of users with a certain role?
You should create a view with filter criteria "role" then you expose it and allow multiple selection.

Then you can create an header or footer (always in view) and add this piece of code

&lt;?php
  $view = views_get_current_view();
  print $view-&gt;total_rows; 
?&gt;


You should have the php filter enabled.
This works for me.