I had 3.1 working with VS 2008.
I decided to uninstall VS 2005 as I no longer need it.
3.1 no longer appears in the Add-in Manager in VS 2008. I installed 3.1 and VS 2008, rebooted and installed again. The Resharper menu is there, but most of the items are ghosted. The Add-in Manager lists nothing as well.
Even the About menu is ghosted in the ReSharper menu.