The Blender exporter lets you publish 3D files straight from Blender to Sketchfab.
As of Blender 2.70, the Sketchfab exporter is natively integrated! As long as you have the latest version, you can already export your models directly from Blender.
It will give you a link to the new model when it's ready. You can continue working while waiting. When the upload is complete, you can view your model on Sketchfab, adjust rendering settings, and save the default view.
If you prefer to use an older version of Blender, you can still manually install the addon.