I've been studying for about two years, the first 9 months of which were quite informal (read: I sat down with 30 volumes of Ranma 1/2, pen, paper, and a dictionary and tried to pick out patterns). Since then I've taken a total of 6 Japanese courses, and recently took the JLPT Level 3 (if the practice tests I took last semester are any indication, I just passed it...we'll find out in about a month or so, ne?). All the while I've continued to do such things as read manga and watch anime raw, which has helped immensely (I know roughly 700 or so Kanji)