As some may know, I use Hotmail's inbox interface for all of my Techman's World inboxes (unless a user decides to upgrade on their own) because it offers better display of a site's custom logo, in this case it's the Techman's World logo. For everything else, I use Outlook.com.
After checking my email for Techman's World today I got two real forms of warnings asking to upgrade to Outlook.com before I'm forced to do so, and of course the normal advertisements trying to get you to upgrade.
Hotmail users who sign into their accounts or access their inbox's will get a popup that looks like this (click to enlarge):
For now, you can choose "Maybe later" and move on with your day, but I'm sure that soon enough you'll find yourself in the new Outlook.com interface, and you can't change back. If you choose to upgrade to Outlook.com, be advised that you can't switch back to Hotmail. Basically, once you upgrade, you upgrade. There is no turning back.
You'll also get a warning banner at the top of your inbox, where usually you'll get "ads" about using Internet Explorer, contacts, and so on.
So, pretty soon the Hotmail to Outlook.com switch will happen. When do you think they'll flip the switch?