Maxis announced Sandbox Mode today, allowing you to (if you want) create a region where you can cheat, get infinite money, turn off fires and disasters, etc.
I expect a lot of people will use this mode to goof around and plan out things they want to try in normal mode.
You can't participate in challenges, achievements, and leaderboards obviously with this mode but I think it is a useful addition.
http://www.simcity.com/en_US/blog/ar...y-sandbox-mode
http://www.facebook.com/SimCity