Instant messaging is nothing new – we’ve all been using Yahoo, AIM and MSN chat for donkey’s years. But the proliferation of Ajax in web pages has changed all that.

Ajax’s main advantage is that it enables small amounts of information to be exchanged with the web server without refreshing the entire web page. 

Google’s chat facility in GMail (Google Mail) has been a key advocate of this, with multiple chat windows overlaying your GMail view, unaffected by actions such as clicking on folders and replying to mails.

Now Facebook has got in on the act, placing an icon in the bottom corner of any Facebook window. Once you click this and go online with chat, it becomes a long grey bar along the bottom of the window. You can choose to look at the latest notifications or see who’s online.

Too addictive?

This works surprisingly well and isn’t too intrusive, which we thought it might well have been  - although we still think you’ll find it pretty addictive. Mind you, it’s perfectly possible to pop a chat out of your Facebook window if you want it separately. That means you can close Facebook itself and still have the chat window open should you wish – that’s better.

The basic chat works in the expected way, with double-clicking on an online contact to begin a chat. You can also go offline at any time you choose as well as minimise conversations to the bar to keep them at bay. Chat histories are stored for a short time, but you can flush this out after every conversation should you wish.

"Conversations are one-to-one, completely private, and only between Facebook friends. The message history is saved from page to page, and even between login sessions, but it is not logged permanently," explains Facebook engineer Josh on the Facebook blog.

Other than that, features are currently limited but set to grow. There’s no group chat, but you can have several chats simultaneously. You also can’t block individual users. This may seem limiting, but we’d guess that if you don’t want to chat, why are they on your Facebook profile in the first place?