As far as other IRC clients, I'm not sure how they do it, but because they are mostly all a LOT less used than mIRC, they can all hammer the servers and the servers probably aren't going to mind too much. If mIRC started doing that from every client out there, the servers would probably have a fit because there are so many mIRC clients out there. That's assuming that they do "hammer" the servers to maintain away statuses. Perhaps they only update away statuses every X minutes or something like that. Not accurate, but easier on the servers.
In the early thru late 90's mac clients used userhost in groups every 30 seconds (25 nicks at a time) and would repeat this for every channel in five minute intervals. Over a 2,400bps PPP connection there was no noticeable latency. Hence it is highly effective. The /who #channel alternative was completely unacceptable under these conditions. 2,400 bps limits you to 300 characters per second.
Of course today using /who #channel every five minutes is the defacto choice because scripts have been doing it for years. The impact on the server is negligible. Even every client doing this repeatedly every 5 minutes would put little strain on a server. And the /userhost approach won't put ANY strain on the server.
I've brought this up before and people always refused to accept the /userhost approach. Probably because like so many IRC users they really thought they new *everything*. And it's not easy to script. But it pretty much foolproof.
People set /away all the time, btw.
