Hi Katy,
I'm also hoping for Ethiopia and Iran at some stage! Fingers crossed!
Cheers,
Bob
http://www.state.gov/r/pa/prs/ps/2016/01/251577.htm
If you've been to these countries you can only visit the US by going through a full visa process at a US Embassy with all of the necessary faff and cost that will go along with that. I just renewed my ESTA for a work trip to the US and there's now an extra question on this along the lines of: "Have you travelled to Iran, Iraq, Sudan or Syria since 1st March 2011 inclusive, or do you intend to before your travel to the United States?" If you answer yes, you don't get approved.
If you never intend to visit the US again then it's not a problem in that case.