So, are these two well-known bugs related?
Half the time when I try to log in today, the launcher hangs at "loading launcher".
The other half, when the launcher actually loads, it tells me that my username or password is invalid. Now it'd take a brute force attack about 90 years to guess my password, as a non-dictionary alphanumeric string of reasonable length. And I use different passwords for everything, so they can't have hacked it from another database. So I'm guessing as with most people who experience this in the forums, it's down to the game randomly deciding not to recognise my existing password all of a sudden.
Just made my 30th attempt this morning, and it logged me in. So it definitely is a glitch with it just deciding not to recognise my login details for some reason. Maybe an issue with connection between the client and server?