I am currently in the process of opening a rep office and thought I would share two points, since there were some uncertainties in past posts
Legalization of incorporation document is NOT required anymore
Local notarization of POA is the preferred method
Source: Through a contact at Deloitte Taiwan I got this information:
which confirms above summary. I have also been at the MOEA myself a couple of days ago and confirmed this once more. When you can write the POA yourself (you are director of the foreign company) and you are already in Taiwan, do it here.
Sorry if this has already been clear to everybody, I was confused before and thought sharing it would be a good idea 2013 update