Have you participated in subject-specific Olympiads?

I don't like olympiads – my school life is already too busy. But I always participate in English language olympiads (firstly, for the certificate required for university admission, proving a high level of language proficiency (in grades 9-11), and secondly, for self-assessment). Our school olympiads are conducted as City & Guilds tests, so I participate with pleasure (to avoid any misunderstanding, the City & Guilds center issues international certificates).