Oh no please! 'Obrigado' doesn't sound forced. On the contrary, it's the most common word used to say thanks in Brazil. Someone please correct me if I am wrong, but I think is the most common word used to say thanks in all Portuguese speaking countries.

'Brigado' is ok if you are in informal conversations with your friends, but in the other situations, sounds really ugly in my opinion. Words for gratitude are always polite, no matter if you say:
- obrigado/a
- muito obrigado/a
- muitíssimo obrigado/a
- muito agradecido/a
- grato/a
- muito grato/a
- agradeço-te
- obrigadinho/a (informal)
- Obrigadão! (very informal)
- Valeu! (very informal)

Gostei! Hoje eu aprendi o uso como interjeição e substantivo. Na verdade para os estrangeiros que falam línguas como o inglês que não tem distinção do gênero nem do número é dificílimo.

Great article! However, my Brazilian partner says that I need to say 'brigado' to people, as 'obrigado' can sound a little sarcastic or forced.

One of the first words I've learnt of Portuguese language was "Obrigado". I think it's impossible forget this word :)

It's clear and a good explanation of the difference between male and female words, who is often a real difficulty for the no latin. Obrigada Li :)