We never feel that machine tranlsation lower rankings. In fact we felt the opposite - translated pages brings more users and start miltilanguate discussions.

When spiders are crawling your page they take text which in next step is indexed. It means that your content is remembered in whole and in parts - using complicated algorithm scripts are ranking your content by separate words. Script is not able to tell does your content is created by men or automatically translated, especially that vBET supports manual corrections. Scripts are not able to tell it, because translated content is created by scripts itself - you have in your content the best what script can do in area of text analyze. So going this way this suppose to be the best content to index for scripts\programs, because it is in form which script understand best - it is generated by scripts.