I took private lessons from my instructor. While I agree that the instructor can help point out, in precise detail, where your aikido sucks, I feel the most invaluable part of the process is taking ukemi. Being able to see and feel his application of aikido, and being given the chance to try to find weak points in his technique, has been a great learning experience. Always take the opportunity to get tossed around by an experienced and skilled aikidoka, especially if he/she is letting you be uncooperative. My 2 cents...