You can login as many times as you want on all different devices. The limit is on how many devices may play video at the same time. This is testes in Scandinavia. You may play on the same account on two devices at ones. Otherwise you will run into this error:
Whoops, something went wrong…
Netflix Streaming Error
Your Netflix account is in use on too many devices. Please stop playing on other devices to continue. Visit netflix.com/help for more information.
Error Code: N8107-154-5006
Read more on the error here: http://support.netflix.com/en/node/137#gsc.tab=0