From what I understand it can be a problem if you don't keep the database that holds the IP addresses of the spiders/robots updated (weekly / daily ? what do people recommend?)
If this list was not updated regularly enough then I assume that a new spider or a spider with a changed IP address would get to see the page that is output to human users.
Would this ever lead to you being blacklisted by the Search Engines. I would have thought the only problem with this would be that your un-optimised 'user' pages would be ranked lower. I cannot see that this should cause a blacklisting but there is much talk on this forum about being careful when starting out in cloaking for reasons of being blacklisted. Can someone please clear this up for me.