Which languages are easiest -- and most difficult -- for native English speakers to learn?

Thankfully for language learners today, the US Foreign Service Institute's language books and tapes can be found online.
These are the best free courses available, though you can still detect a touch of the Cold War in the syllabus ("Where is the state clothing shop?").
Best of all, the FSI has done us a great service by classifying languages in degrees of difficulty for English speakers.
Here are a few examples, ranked in order of the number of hours it takes the average learner to master them from lowest to highest:

Easiest (about 600 hours of study)

After just 600 hours of study, you'll have no trouble fitting in on the streets of Paris.

Which languages are easiest -- and most difficult -- for native English speakers to learn?

...a French "préservatif" is not something you add to your food, but a condom...