Actually we had to remove a couple of openacs.org pages from Google's cache about three months ago - I won't go into details, it was a legitimate request. To add to Jerry's information you can request they reindex your page (therefore seeing the metatag and doing the removal) via the web so it's easy to do.
robot detection was working somewhat in 4.6, though I had to track down the new home for the information (which may no longer be the best home).
