If I am not wrong the Second Line in the Compiler.class.php is useless.

<?php
$compiler = 'lessphp';
if( defined('WP_LESS_COMPILER') ){

The $compiler variable is never used again, is it?

Secondly, would it not been better to register a filter hook to let programmers change the folder with the compiler class base, instead of using globals?

Also would it not been better to encapsulate the checksequence for the includepath inside some other class? This plugin is nicely done in OOP but that look outside the norm.

I just used to switch from lessphp to less.php 'cause lessphp does not compile the "Semantic Grid System" less files right.
Was nicely surprised that switching the compiler class was soo easy! :)
Many thank!