Cartridge aging and tip wear symtoms?

While I appreciate all the above answers, I am still left confused as to how to recognize the onset of cartridge failure. I agree that if the suspension fails then the results will be probably obvious. However, what are the symtoms of failure of the diamond tip? It seems a little strange to have to remove the cartridge every so often and check the diamond under a microspcope. Assuming that wear is evident under the scope, how long has this been accruing and how much damage has already been done to the record.
If one could recognize diamond wear when it begins and knows the symtoms, it seems to me you could minimize or prohibit record wear.

Diamonds wear very slowly! By the time a diamond would have any significant wear, you would have noticed mistracking *long* before!

Record wear is primarily caused by mistracking- but rarely by a worn stylus! Far more common issues are poor tone arm setup and hardware that is really not up to the task. It is also not a good idea to play an LP more than once in 24 hours, so as to allow for the vinyl to rebound. If you think about it, the amount of pressure that a needle exerts on the LP is prodigious- once you work it out to weight per square inch.

Stylus wear or deterioration of the rubber suspension parts will be most evident from tracking problems. If you hear the music breaking up or sounding sibilant where the sound was clean before, some kind of wear or deterioration may be manifesting itself. A test record with music passages with increasingly higher modulation levels (loudness) are helpful, assuming you can recall how well the cartridge performed on these tests when new. Loud passages, with a lot of high frequency content, particularly toward the inner grooves of the record are the most difficult to track and should show up incipient problems first.

Most microscopic examinations can only detect really gross damage/wear. I've had cartridges examined that were obviously going bad that showed absolutely no wear even when examined under the proper kinds of stereoscopes. The only pictures I've seen that clearly showed subtle wear were those made by scanning electron microscopes and no shop would have access to that kind of gear.

I would go with what I hear to make the call as to when the stylus needs to be replaced.