Using the current release of Blender 2.78 with Linux Mint (Cinnamon, 64-bit), and having problems with the exporter plugin for Blender. (The one included with the Blender install.) Used API key from user profile.
Tried again using the "Claim your token" button, which also had an error:
Import error: No module named 'requests'
That's followed by the file path for the sketchfab addon folder and ___init__.py, with some reference to line 400. (Can't seem to copy the error message directly, sorry.)
File is of a basic environment scene. Haven't uploaded it through the browser at the time of this post.