You need to clean your bobbin area (including taking off the throat plate and getting the lint glob from under there) periodically. Those who feel it is needed after every bobbin are probably sewing with linty thread. Switching to a less linty thread will have the added benefit of not linting as much. As for changing the needle, I agree that the new titanium needles are a good value in that they last much longer. Keep in mind that even a "new" needle may be defective -- I've heard as much as 1 in 5. Skipped stitches, a punching sound, and any time you hit a pin are signs that you should change the needle. I don't follow the 8 hour rule, but I don't go weeks, either.