The service is available for new users, and existing Hotmail and Live users can also migrate across and use the new interface.
Microsoft tweeted that it has had 1 million signups to the new service (its not clear if this is new accounts only, or includes people migrating across from Hotmail and Live or securing new aliases).
Of course many of these users will simply be securing their name, but its still a massive opening day response.
And the service looks to be worth it. The new interface is very clear and Metro like, there are currently far more subtle advertisements taking up less space than there are in Hotmail and Live, although it remains to be seen how long this lasts.
The service offers improved integration with SkyDrive and Office documents can be viewed and even edited simply within the interface. Also with the optional Twitter, GMail, LinkedIn and Facebook integration instant chat is available on the right side for Facebook Chat or other Outlook users.
Existing users can secure a new @outlook.com name and hold it as an alias (recommended) or migrate fully across and start using the new address solely – not recommended at this stage.
Skype will be coming to Outlook.com soon, so people can video call Skype or Outlook friends, even if neither have the Skype client installed.
If you have a Windows Phone handset and setup the primary account as your Hotmail / Live ID definitely do not fully migrate across to your new Outlook.com address (secure it with an alias) as this will mess up your Windows Phone requiring a reset.