Just tried out Thinking Worlds, which is being developed as a tool for use in Uk schools http://www.thinkingworlds.com/Home/tabid/113/Default.aspx
The interface is pretty good. The worlds/environments I visited were very good - much better than on SL. i also managed to move around very easily (use of mouse for movement is coming later in the year).
However I found the pre-made games too basic, when they worked at all - eg read a text and answer true or false questions over and over in the Domesday Book section. The bullying task did not work but appears to be a similar game. The marketing one confused me and I ran out of time - if anyone works out what to do drop me a line.
However I can see that this has great potential. There are already activities uploaded for Science, ICT, History, English Lit etc.. I assume the use of different avatars etc will be developed too. I managed to change my character once but the change wasn't saved. With some good fixes as it is developed - and hopefully an easy authoring tool I can see this being a great tool in future, and more especially because it is not slowed down by thousands of other internet users on the servers (as in SL).
I have not tried the authoring tool yet.