Stealth Attacks

What are stealth attacks, what difference does it make to attack someone?

It's a attacking option, you can try to "Stealth" attacks and depending on your stats and the targets stats you might appear as "Someone" in their attack log.

....so they don't know who attack them.

That's pretty much about it.

This is very useful, for mugging people. So u don't have to get a bounty, or something.
Also, stealth is all about how much dex u have (plus ur merit points spent on stealth).

And some job specials affect stealth as well..

Its mostly about your dex vs the oponenets dex but merits and job specials could tip the balance in a close call.

When I first joined up I thought there was a setting on whether you wanted to be 'someone' or yourself. Is that no longer the case?

You can still choose to have attack stealthing on "whenever possible" or switch it off.

The whenever possible will then stealth if possible using the criteria given above in other replies.

When you switch stealth off, it will be off regardless of other criteria

Thanks everyone, makes sense now. Although it would be interesting if a 'stealth' attack gave you an extra attack or something similar.