After Updating my Lumia 1020 to Windows Phone Developer Preview version 8.1 I felt the new features were great. However, I encountered what I consider a terrible bug, approximately every few hours my phone would not respond, it could not be opened and would require a soft reset every time in order to gain access.
I believe I have tracked this down to the password lock. After removing the password lock I am no longer experiencing this issue. Clearly no-one at Microsoft tried putting a password on their phone, developer preview or not this is a bug that really should have been high priority and not made through any reasonable QA process.
Still feature wise WP 8.1 is great and if Chrome comes to the platform then I doubt I would leave.