The act covers pretty much everything except when there's a valid reason to not hand the information over, such as official secrets or confidentiality. These "exemptions" are Absolute and Qualified (like privilege). Absolute exemptions relate to official secrets, the Ministry of Defence etc. Qualified exemptions are for things such as ministerial communications and commercial confidentiality. Whilst these are a hinderance as a journalist, there are still plenty of opportunities to uncover great stories due to the FOI Act like the expenses scandal.
Many journalists see now as the Golden Age of the FOI. There's still a treasure trove of information buried away, waiting to be enquired about. In order to combat this, politicians are no longer writing things down to avoid it being "on the record". Such 'on the sofa' politics has allowed for informal chats as opposed to formal meetings where minutes etc have to be kept.