An (potentially) improved loadClass method for the PSR-0 autoloader that eliminates naming collisions at the (potential) sake of performance. Untested.

loadClass.php

<?php

    public function loadClass($className)
    {
        if (null === $this->_namespace || $this->_namespace.$this->_namespaceSeparator === substr($className, 0, strlen($this->_namespace.$this->_namespaceSeparator))) {
            $fileName = '';
            $namespace = '';
            if (false !== ($lastNsPos = strripos($className, $this->_namespaceSeparator))) {
                $namespace = substr($className, 0, $lastNsPos);
                $className = substr($className, $lastNsPos + 1);
                $filePath = str_replace($this->_namespaceSeparator, DIRECTORY_SEPARATOR, $namespace) . DIRECTORY_SEPARATOR;
            }
            $fileName = $filePath . $className . $this->_fileExtension;
            
            include ($this->_includePath !== null ? $this->_includePath . DIRECTORY_SEPARATOR : '') . $fileName;
            
            // Check if the actual class has been found, not just it's supposed containing file.
            if (class_exists($namespace . '\\' . $className, false) {
            	return true;
            } else {
            	// If it's not found, try to load it again, this time replacing _'s as well.
            	$fileName = $filePath . str_replace('_', DIRECTORY_SEPARATOR, $className) . $this->_fileExtension;
            	include ($this->_includePath !== null ? $this->_includePath . DIRECTORY_SEPARATOR : '') . $fileName;
                
                if (class_exists($namespace . '\\' . $className, false) {
                    return true;
                } else {
                    // STILL not found? Give up.
                    return false;
                }
            }
        }
    }