The word I hear is NJ, NY, California and Florida are the pains in the butt; expensive, and a long wait.
Most states you usually get the license in a few weeks tops and it's a few hundred dollars. NJ, you wait several months, possibly even around a year and it costs around $1000.
The supposed reason is the above states have something about them. NJ/NY have always been overloaded with bureacracy, California too, and the word on Florida is every freaking doctor there wants to vacation there or in semi-retirement and wants to get some gig where they do locums, and because of that the state can't adequately track how many doctors they really have full-time. For that reason they make it hard to get a license.
Now this is based on colleagues telling me their experiences, so anyone here really know how it works for real please feel free to correct me.