I took it for a year and a half in college (one semester was intensive), and I spent about a month in Sapporo on this mini exchange thing my college offered, but I felt like I was hitting my limit with the thing. Basically, I could do tests and homework and the like well enough, but I had a lot of trouble actually conversing with anyone, and it was a bit frustrating to see the one person who went over knowing virtually nothing being able to have a conversation better than I could by the end of our time in Sapporo. Around that point, I was able to get the gist of what was going on when I played of Dragon Quest III and Fire Emblem Gaiden with a dictionary, but it was really slow. It's been over five years since then, and I've atrophied a bit, but I can get around menus in games pretty easily.