Yes it does mean "it doesn't interest them" and we use it a lot in Ireland.

Yes, it is common. And I beg to differ with lollykh. It IS common in the United States as well as the UK. In the United States, we don't drink tea, we drink coffee. <---Note, crazy exaggeration Nevertheless, we often use the expression "not their cup of tea" or "not my cup of tea." (And we NEVER EVER EVER say "That isn't their cup of coffee!")

It means it's not to your taste. For example, if you have just been to an exhibition of modern art, and your friend asks you what you thought, you could say: 'Hmm, it was interesting, but that kind of thing isn't really my cup of tea'. And yes, it is quite a common expression.

Yes it means 'it doesn't interest them' or 'it's not their style'. And only common in the UK and Ireland.