With the introduction of the Nexus 4, Google has added “Photo Sphere” support in Google+. Here’s an example. Google’s viewer could use some work, but as it’s a new feature, it should improve over time. Since the only thing that makes a photo a “Photo Sphere” is a bit of XMP data, one can easily make a panorama stitched with other software, such a Hugin, a “Photo Sphere.” Here’s a short Exiv2 command file to add the required information:
Just change the heights and widths to appropriate values and run it to make a full equirectangular panorama a “Photo Sphere.” There’s also support for partial panoramas, but I haven’t looked into it as the Nexus 4 hasn’t even been released yet.