The phrases.org.uk website gives very good explanations for common expressions. http://www.phrases.org.uk/meanings/my-cup-of-tea.html Do we use it? I've heard some teachers say that it's only used in an English-learning context; students learn it but modern English speakers don't really use it. The truth is, we all recognise it as a common expression so don't be afraid of using it. One of my close Aussie friends uses a shortened version: "it's not my cuppa".

Here in Mozambique, We often use it like: "Não é minha praia". Q: Do you like playing game? P: Gostas de jogar? A: It's not my cup of tea. R: Não é minha praia (No sentido de jogo, mas nem tanto. Não sou bom nisso) A: I'm learning English, because I want to apply for a scholarship next year. How does that grab you? B: That's cool, I wish you all the best. But, as you know English is not my cup of tea so I'll do my Master Degree here.

"It's not my cup of tea," means that it's not something you enjoy, or are interested in. I hear the expression every once in awhile, not too often.

it's not my cup of tea = it's not my thing/it's not for me/it's not what I like to do. It is used a lot, both in the US and UK.