There are a lot of educators using Second Life and looking at possible ways that this and other similar environments might be used to improve teaching and learning.
While not every use is really suited for the 3D environment occasionally there is across something that uses the strengths of the space well. SciLands is a mini-continent devoted to science and technology, and one of the things it contains is the Solar System Tour which aims to demonstrate the massive distances in space - something that isn't easy to do in 2D.
If you're new to Second Life you can sign up for free, read 'The Unofficial Complete Fool's Guide to Second Life' and subscribe to the SL Educators mailing list. To look at other educational uses of SL watch 'Educational Uses of Second Life'.
I'm in the process of trying to calculate what sort of costs occur (time and money) to both Edge Hill staff and students when creating and accessing various resources and learning experiences in this environment and other similar ones. This will help us make decisions about what we can try to achieve if people want to use the technology.