I just installed Build 10041 on my Asus Vivotab Note 8.  Everything was going fine until it came time to enter my Microsoft Account.  Some weird things happened, screen flashed a few times and then rebooted.  After it rebooted a screen came up asking me the password for "defaultuser0".  I've tried both no password and my normal password for my Microsoft account to no avail.  Any ideas what the password would be????

Yup. Got the same behavior.

Some tard at Microsoft let this out into the wild without installing it. Worthless build if you can't get logged in.

There is no default password for Windows 10 TP.  You need to reformat your drive and install the official Windows 10 TP Build 10041 bits:  Download links

CF

Clean install from legit link yields a default user 0 as shown on all 3 of my machines

I see the same thing when opening winver but there is no "defaultuser0" account per se on my PC.  I entered my Microsoft Account information and password when prompted to do so during the setup phase of the installation. 

I have both a local Login and a Microsoft Account Login. My Winver shows as registered to the Local Login user even though I have been logging in with a Microsoft Account. 

Please review this KB article: The user name and password box might not appear on the sign-in screen in Windows 10 Technical Preview