I emailed Aramburu restaurant ( http://www.arambururesto.com/ ) one full month in advance, based on the recommendations in this board.
Keep in mind this is a "reservations only" place.
My email remained unanswered.
I called 2 weeks prior to my trip, spoke with the owner Gonzalo Aramburu, who personally took the reservations.
Once in Buenos Aires I emailed to confirm.
As usual, email unanswered.
I called to confirm.
Friend keeps trying.
Finally, an answer : we're close for remodelling.
Friend insists: "but you took the reservations...?"
Answer: hung up.
Sorry folks, but this guy has no idea how to run a place.
His food might be fantastic, but as far as I'm concerned I won't retry.
Plenty of (serious and) excellent places in town.