Originally posted by Ron Boggs k100d hit it on the head. I have always sent my film bodies in for CLA after a year of use. Presuming all was well in the CLA, then maybe every 5 years. With my several digital cameras...use 'em 'til they die. Haven't ever sent one in..., though if I purchased one used, I'd send it in before trusting it...So digital bodies are "disposable" like a Bic lighter...no service necessary (I'm sure someone else will set me straight on this).
CLA--cleaning, lubrication and adjustment--basically means checking that everything is working at factory specs. Meter accurate, shutter accurate, mirror mechanism working correctly, seals intact, all systems functioning, plus a going over for dust and dirt...
I've sent several lenses in, but always when service was needed--slow aperture blades, screw loose, noisey focus, etc. Never sent a lens just for CLA.
dSLRs do need CLA as well. The SR system, AF system, and other parts all need adjustment over time, as well as lubrication on many parts. The owners manual for the K20D tells you in the first few pages to send it in every year or two to have it checked to make sure its up to factory specs (lens as well). Also the Pentax extended warranty gives the owner a free tune-up, which is as you say CLA and to make sure its up to factory specs. Unfortunately there are many moving parts inside a dSLR that will fall out of spec over time. Don't believe me, read the owners manual, and or call Pentax. Since I have the free tune-up I will do it, but if I did not have the free tune-up I would probably do like most and only wait till there is a problem then have it serviced. This all depends on your use, if you only put say 5000 clicks a year on your dSLR forget it and keep shooting. If your a heavy shooter like me and will have 30,000 clicks a year... CLA/tune-up should be done to keep your investment going.