I've just been testing out Campfire, the new web-based chat service from 37Signals. As you'd expect, it's simple, intuitive and good looking. It's really a service for small businesses who want to keep all their chats in one place (all chats are permalinked) - you can also insert images in the chat window itself, which is a nice touch. For one-to-one chat, it's only marginally more useful than your IM client - where it really shines is for multi-person chats. And yes, it does take a lot of the pain out of organizing group chats and having no centralized place to store them. The key features:
-Every chat has a permanent URL
-Campfire chats don't require special chat software or networks
-Instantly share and discuss files with your colleagues/clients
-Search or browse through transcripts of past chats
-Chat securely over SSL (Plus and Premium plans)
Still, this feels like a Writeboard to me - something that only becomes truly powerful when it's integrated with the other 37Signals products. Once that happens, 37Signals will find themselves with an extremely useful suite of services for small business communication.
PS. One issue I had was that it didn't seem to work well with Opera - using a minority browser has its disadvantages.