Anyone else have trouble signing into the editor after installing? I receive a 'Service not available, please try again later.' message. I have an internet connection and am not using a firewall. I tried disconnecting my network to try to manually sign in, but I received the same error. Edit: in /opt/Unity/Editor/Data/Resources/Home/src/pn-login/login.js there is a reference for signUpUrl that points to https://unity3d.com/sign-up, I get a 404 error if I try this page, does this need to be updated?
I was able to sign in yesterday with no issue (afternoon). I'm running the latest build, are you running it too? I tried the URL link you provided, I'm also getting a 404 error.
I had unity-editor-5.1.0f3+2015082501_amd64.deb and then I installed unity-editor-5.1.0f3+2015091501_amd64.deb
Was able to register by using the offline method, as in this post http://forum.unity3d.com/threads/manual-activation.355761/. I tried before by unplugging my network cable, but I had to manually bring down my virtualbox connection as well.