Hello Mark:
 
There is general user maintenance that should be performed on all vacuums regardless of make and/or model and cost.  You know what they are:  Belt changes, bag and filter changes, filter cleanings and so on.
 
There are parts that wear out, break, and mal-function that have to be replaced.  Do it "as needed."   Switch, cord, hose, brush roll, bearings, fan, bulb, wheels, and so on.
 
Motor service?  Depends.  Do you have an expensive vacuum that you want to work well for 10-20 years?  Yes, by all means take it to a reputable store and have it looked at.  How often?  It depends.  How often do you use it?  Most owners will take their favorite high end vacuum in on a regular bases.  Every year/two.  Just to make sure it is performing like new.  When they do, the routine maintenance items will be replaced usually too.  Some will wait until they experience a problem and then get it done.  Your asset, your investment, your call.
 
If you have a cheap big box brand: Do you need motor service?  Probably not.  Just use the vacuum until the cost of ownership (and repairs) exceeds the cost to replace it.  And start all over again.  This latter trend in appliance buying by US customers, with vacuums probably starting in the 60's, launched the beginning of the disposables and throw aways.  (I don't say that in a bad way.  Just as a fact.)
 
Carmine D.

Quote from old-timer on 04/07/07 at 4:20pm:

 
All of this is necessary on all but Dyson.  They just need a filter cleaning.  I may run some injector cleaner through it once a year.  How ya doing O.T.?