Making it harder to read/steal, eh?
You could simply strip out all the line break characters (\n and \r)...
$source = str_replace(array("\n", "\r"), "", $source);
Of course, that may cause problems if you need line breaks in your code (like for a <textarea> or <pre>). Also, any tabs or spaces used for indenting would still remain... you could probably use a regexp to get rid of those...
/ 
