Product classification codes - UNSPSC/CPV

Does anyone have experience with product/material classification taxonomy like UNSPSC, CPV etc? More specifically I am interested in knowing how do you currently assign product codes and how pressing a problem it is for you guys. At the moment I am having to manually lookup relevant codes and then assign it. Are there any tools that you use? And also how easy do these tools make it for you to classify products/materials. Also do you apply these codes to invoice descriptions or any other sources of data?