I take mine in once or twice a year, usually just before a retreat. I used to take it to the local Viking place, but most recently I took it to my favorite quilt store, which is a Bernina dealer, but services most brands of machines. The good thing about them is that the repair guy works out of the shop there and is in every day. I dropped my machine off at lunch and they called before 5 to tell me it was done! The Viking place is essentially a drop off location for a traveling repair man and it takes a week or more to get back home :-(.
So I'm probably going to skip the Viking place and take it to my fav. quilt store from now on. My machine is a mid-80's Viking Husqvarna 990 SLE.