In practice, the scoping difference that you run into 99% of the time is that implicit var keywords are in front of variables that haven't been seen in the current scope, and you have to assign globals to your top level scope (window in the browser). How long did it take me to bridge that separation from the original language? Oh, about a minute.
I've made a one-time investment of a minuscule amount of time and have been raking in the saved time and effort from not having to type var statements or track down lack-of-var bugs.
