how many hours?

with a welly kept setup how many hours can you expect from a mm or mc? 10000? 1000?
There are so many things that effect this that it is very hard to say, stylus cut, alignment, tracking force, cleanliness and condition of the records being played, bearing friction in the tonearm, etc. I hew very closely to the time span given in the Ortofon FAQ which is 600 to 1000 hours:

I hear figures of 3000 hours from those that have invested a lot in their cartridges, but as a practical matter, find these to be fairytales. Note though, that a cartridge does not just fall off of the face of the earth but wares fairly linearly, like a set of automotive tires.

I am sure that you will hear longer lifespans for cartridges, and should those who claim this be correct, you will be throwing away some money by replacing your stylus too quickly should you listen to my advice. However, if Ortofon is correct and you do not heed this advice, you will be compromising your irreplacable record collection by subjecting it to excessive wear. I usually err on the side of caution.
I have heard from 1500hrs to 4000 hrs for a good moving coil. 600hrs would be about 4-5months life for some people I know and I have never heard of anyone wearing one out that fast. Clearaudio has a two year warranty on thier MC carts and recently advised if properly taken care of and set up 3000 to 3500hrs. My shelter 501mk II was inspected at about 1500hrs, (2 1/2 years) and it looked good with pleanty of life.
Your talking about how long it takes to wear out a diamond by rubbing vinyl against it. I think it's much more likely that you'll damage the cantelever by dropping it or knocking against the table at some point. The only times I've had to replace a stylus was when I damaged the cantelever or just got bored with the cartridge and wanted to try something new.
I use Stylast #5 stylus lubricant. The manufacturer claims up to 10x extension in stylus life. While I cannot confirm this claim, at 2000-3000 hrs. my Helikon still sounds great. Of course eventually the compliance of the suspension will fail due to wear or aging rubber.
interesting...all very informative posts.