When I'm chatting with someone that has their away set, kopete repeats:

#  [Nick] is away (Gone, for more info use WHOIS [Nick] [Nick])

every few seconds. This is incredibly annoying since the real messages get lost in the endless stream of useless away messages. If my conversation partner chooses to be "away", that his/her choice and there is no need to bug me with it all the time. So my question is: How on earth do I switch these messages off???

This is likely because Kopete is performing some check with their client which causes it to send back that message. Please file a bug at bugs.kde.org, please make sure to include information on the protocol you are using ( and if the other person is using the official client )