For atleast 12 hours it has been slightly difficult to sign up for a Twitter account.
As Wim Geerts says in this tweet, http://twitter.com/signup actually links to https://about.twitter.com/mobile-signup and there is nothing to signup :-(
You can choose to get an app, but if you have a computer with older version than windows 8 you are screwed. Atleast for now.
If you should do a search on Twitter and get a result, you will see a signup on the left side of your screen, but entering any information will only take you back to https://about.twitter.com/mobile-signup and not sign you up for anything.
Maybe you will get updates from Twitter, because you have after all given them your emailadress in the failed signup attempt.
Too bad if you wanted a Twitter account right now.
You can always use your mobile phone and give it a try, but I have no idea how it will work if you already have an account and wanted to register a second account.
I feel pretty sure that things will change in the near future and signing up for Twitter will become easy again.
Meanwhile it's just annoying.
Hope you have a great weekend.
Have Fun :)