Originally Posted by Maelochs

One thing you can do is go the the manufacturer's site and look at pictures of a new cassette. If a cassette is really worn some of the cogs will be much pointier, scalloped .... depending on how you ride, usually the biggest cog or the smallest will get least wear while the middle ones will gt more ... but it is unlikely that every cog will wear the same. So .... look for the least and most worn looking cogs.

If the chain isn't skipping I'd imagine that your cassette is fine. if your chain is skipping i'd imagine that you would need to adjust the derailleur.

I figure three chains per cassette ... but if you keep everything clean and aren't riding really hard, maybe more ... and less, obviously, if you do ride hard or don't do good maintenance.

Unless I am just making up all this stuff to feel important on the Internet.

Welcome aboard.