I have a Bernina and should do it annually but it seems I only get it in every 3 years or so. :shock: I have been fortunate that I have suffered no ill effects of my infrequency and have never had the dealer say anything to me that he found out of the ordinary or that it was overly crammed full of lint anywhere. I clean and oil the bobbin race area every 3 bobbins. Thankfully I just got my baby back from servicing so I am good to go until next summer.
ETA: It also makes a difference how much the machine is used. I do not sew daily and since getting my LA I do very little machine quilting any more on mine. I am sporadic with my peicing and really have not had a chance to do very much since getting my LA.