With smaller or less busy forums it can lead to the main threads almost being made redundant as people use the chat facility instead of posting on the threads. And as storm says it wouldn't work on LZ cos the forum is too busy.
Sticking a chat function on the main page for everyone to use who visits would turn into a mess too quickly, it wouldn't be able to be moderated at all unless someone sits in it full time and that's not what it's all about.
Couple of things though;
The chat function should have a limit to those registered on the site, we have alot of traffic through here, but the majority are guests, on any given day looking at the stats, it's a 70/30% for guests against registered users.
Limit the registered user to 50 posts or more before using a chat function, this will help eliminate the majority of spammers, those who register to post spam within a chat area. Your chatroom name will be the name you use on the forum, not sure how to implement this, but it would be a good idea, again to reduce spam and identity theft ( people pretending to be other people within the chatroom )
The chat shouldn't replace the posts, certain rules, no advisories, should be put up regarding what the chatroom is, link it via the Anything Goes section, it's there as a social area, not as a technical helpline.
Alot can be achieved through the chat option, at one point ( 4-5 years ago ) IRC was the dominant way in which the internet worked until PHpbb forums began to come through, this produced ways to make information more permanent, but IRC still to this day is popular due to it's real time communication, but it's become more popular with ' chatrooms ' which can be monitored within a website.
It may turn out to be dead on it's feet or it may turn out to be popular, but whichever way, it needs to self run itself and have some restrictions so that those who use it are those that regular visit the site as registered users, also it can help bring more registered users to the site.
Another point to add is the traffic regulations through any sub section to the site, i don't know the costs etc and each chatroom on a site has a limit of people able to use it due to bandwidth etc, perhaps a separate server for it?
