Cartridge Break-In

How many hours is generally required to break in a new cartridge? Is there a difference between MM and MC? Is the break-in time generally different with cheaper (under $300) cartridges, compared to the more expensive units?

Does a cartridge deteriorate if not used for an extended time, say, several weeks or a few months?
It will vary by cartridge and manufacturer, but at least 25-40 hours for most moving coils, some will be longer. I really don't have any experience with moving magnets, but I would guess about the same with them. What is breaking in, is mostly mechanical.

A cartridge can deteriorate if unused for very long periods of time, and again will vary from manufacturer and cartridge.

Hope this is of some help.
Here's a tip from the Psychic:

Buy a cheap (99 cents) 12 inch rap or club music single, 45 RPM if possible. Use it to break in the cartridge (make sure the volume is way down!). I play it about 4-5 times per side each day for the first few days and that really shakes them loose...
I don't understand this cartridge break-in process. Why would the cartridge need to be broken in?

Is the tip manufactured with small spikes on it that eventually wear down with use?

If you try and rationalize this I just don't see how time would make the needle play any better. Also what causes the tip to wear? I though it was made of a harder surface then the LP.

Perhaps I misunderstand what you mean by break-in.
Tazuser, haven't you noticed that a brand new car runs better after ten thousand miles than when brand new?

A cartridge is a mechanical device, and the suspension system and coil structure benefit from the first 25 to 100 hours of break in, before it sounds its best.

As for the tip, the diamond does wear eventually, but I have seen this in very few cases. When I worked in a high end audio store that had a microscope designed for examination of phono cartridges, you could actually view the results of years of play. Much more common for the cartridge to be brought in with the suspension or dampers shot, or the cantilever broken off long before the diamond was worn.