Brandon just posted on the Windows Experience blog that Windows Live OneCare 2.5 has arrived in beta form. The software can now be found on the Microsoft Connect site for download. This latest version doesn't offer any major UI updates; instead, the changes from 2.0 to 2.5 are "under the hood," as will most of the changes with the beta going forward.
One thing to note if you're interested in beta testing version 2.5 beta - all the PCs in your OneCare circle will also need to run 2.5 beta you won't see them in your OneCare circle.