I'm going to write a post about my ongoing campaign to learn all major languages every time I finish another one. As I've written before, my goal is to complete the Pimsleur courses for every language I'm interested in, which is approximately 25 of them. Each course is thirty to ninety days long.
I just finished Arabic last night. It was easily the toughest language I've tackled on Pimsleur. There were some lessons where I felt totally lost, but then I'd always catch up within a lesson or two. Most other languages I'd feel caught up pretty much all the time.
Arabic was so difficult that I'm not really sure how much I got out of the thirty days. After thirty days of Romanian I could actually function at a minimal level in Romania. I'm not sure I could say the same about Arabic.
On the other hand, I watched Benny Lewis' 45 day Arabic progress video and I could understand almost the entire conversation. He had a bigger vocabulary, maybe by 50-100%, but our grammatical understanding seemed roughly equivalent, and I think my pronunciation is significantly better. That's a pretty strong testimonial for Pimsleur considering how much work Benny puts into language learning.
The marginal benefit of going from zero knowledge to some knowledge is pretty impressive. I've spoken a tiny bit of Arabic with the owner of my local grocery store as well as a clerk at a drug store. They were both really excited that I spoke any at all.