Ask HN: How have you learned a speaking language?

What resources, methods, etc, have you all used to learn a second speaking language? I've been trying to learn arabic for some time, but have usually hit walls along the way. It's been an on-and-off type of effort, which I realize is probably the worst way to learn a language, or anything really. I'd like some seriously good suggestions. I've tried a few sites out, most of which were usually a pain to use. Is software like Rosetta Stone worth it? What is?