The preview grid has just been updated with what we think will be the final version of SL 1.5.6. If we don't find any blocker bugs* then we will deploy 1.5.6 tomorrow.
A blocker bug would be a new-to-1.5.6 bug that causes a lot of client crashes, sever crashes, content loss, or permission exploit.
We would be thrilled if people could log onto the preview and mess around (make outfits, scripts, try the new features) and report any bugs that they find.