Usa-se "I'm afraid" somente no inglês britânico?

Hello Frederico.

Creio que você possa utilizar essa estrutura livremente, seja no inglês americano ou britânico.

Now let's take a deeper look at it:

I'm afraid is commonly used to present a regretful report like:

- I'm afraid that sales aren't as good as we'd hoped.

- I'm afraid that we're going to have to Joe go (i.e. "We're going to fire Joe")

So, I'm afraid assumes that there will be "sorrow" after whatever statement is about to be spoken/written. The phrase almost prepares the listener/reader for what is about to be said.

As Macmillan dictionary says:

1. I'm afraid is used for politely telling someone something that might make them sad, disappointed, or angry, for example when you cannot do what they want or do not agree with them;

Things haven't been going very well here, I'm afraid.
I'm afraid (that): I'm afraid that I can't accept this job.
I'm afraid to say (that): I'm afraid to say I found the book very dull.
I'm afraid so: 'Did he forget to do it?' 'I'm afraid so.'
I'm afraid not: 'Will John be there?' 'I'm afraid not.'

For some more info, please check those links:
http://www.macmillandictionary.com/dict ... ish/afraid
http://forum.wordreference.com/showthread.php?t=622377


Tha's all from me, man.
Take care!