Why can't I say "Que dia é hoje?", I'm brazilian and for me it has the same meaning.
Is that the difference between day or date? As in Monalday or July 23rd.?
Yes, that's it, I just thought it was weird cause anyone in Brazil says that on a regular day
Why shouldn't 'O que é a data hoje?' be accepted as well?
No, that would sound for us.... a rule?? Well, hard to say... it's complicated to settle a rule =/ hope you learn by the usage...
This video [http://www.youtube.com/watch?v=sdPnfnrASp8] is about "cual" vs "que" in Spanish. I think it is a similar issue.