When you join a channel the server will send the last five messages from the channel to you as raw messages (sent as raw messages so the client can easily hide this feature should the user not want it) so you can catch up.
<abc> XYZ is an idiot!
<def> and he smells!
<abc> oh shh he just signed on!
* XYZ has joined #ABC
Sure it'd probably be a mode set on a channel to enable the logging, but its a bit crazy that you are really offering ANYONE on the network that happens to wander into your channel access to what you've been saying (even if they're banned with services they could well get in before services apply the ban).
If a channel owner (or ops) care about being found that way, they could easily add those same words into the topic.
And if they *don't* want to be found that way, but for some reason continually are, do they put "this is not a help channel" (or whatever) in the topic? I guess that example is more of a problem with people not reading topics in the first place.
