Katharine Berry, a student in the UK, has created an in-browser AJAX application that allows you to log into the virtual world of Second Life, but without all of the laggy graphics. This is a great way to pop in-world for a moment if you just want to chat with other residents, and as far as anybody else will be able to tell your avatar will look just fine (although mostly immobile).
While you can't yet initiate new IM sessions or use the Search functions (these are coming), you can reply to any incoming IMs and participate in local chat wherever your avatar happens to be. You can also teleport your avatar to other locations via an on-screen map, although once there you can't really walk around.
The interface is really simple, really fast, and works in Firefox, Internet Explorer, and newer versions of Safari. You can take it for a quick test drive by clicking here.