I do my Husqvarna yearly, don't forget to take your embroidery arm in too!
I took my old ULT2001 in when I had put on another 5 million stitches. If you check with the service folks, that is what a good portion of them will recommend. If you think about it it seems like a big number, but if you do alot of FSL, it doesn't take that long. Older machines need to be taken care of, as there is more wear on the parts and more chance for fuzzies to attack the innards. It is better to be proactive and let the dealer tune -it up at least annually if you do not use it that much.
The newer machines have a stitch counter within the software of the machine that you can access. (see your instruction manuals for details on your particular machine).
just my $.02
I have the Designer 1 and I take it in annually for a check and clean. The Husqvarna dealer also updates the software at that time.
The machine is too costly for me to risk not doing this.
I do not have a Husq, but heed the good advice of those who do, there's nothing worse than machine problems, mine gets a once a yr maintenance without fail. *
Once a year is sufficient unless you are using it every day, say for running a small business.
Also, get used to the sound your machine makes and then you can spot (hear) trouble straight away and that can save you lots of money on repairs.
I have a Husqvarna Orchidea, the machine is working real good but I still take it in for a service once a year just to keep me happy!