Our office ran into this problem all through the beta, unfortunately looks like the issue is still there in the final release.
The issue is when you try to activate, a dialog tells you there is no internet connection available. I believe this is to do with firewall settings, port 443 and proxies. However after trying to get through our ISA firewall (which is set to allow 443) it doesn’t seem to work.
Seems a little strange given all other Autodesk products have activated perfectly for years, so I’m not too keen on opening ports to try and get it to work.
Not to worry though, there is a workaround. Firstly, get as far as you can go on the activation before it tells you it’s failed. Then go and get a coffee. Come back a couple of minutes later (should only take 20-30 seconds really) and your screen should now be telling you that it’s timed out, and will offer you a link to ‘retry’. For some reason, this link must point to a different method of activation, and works fine, just like Revit 2009 did.
Alternatively if you are a subscription customer, you could try getting the activation code yourself from the register.autodesk.com site.
Hope this helps someone who is pulling their hair out trying to activate Revit!