Now that I have taken the flight, I'll answer my own question, so that it might perhaps save somebody from my own mistake.

Apparently, the ground chaos with TAM is not yet a thing of the past, and seems to be as bad as it ever was. It seems moreover that the cause of the delays has more to do with TAM's poor ground operations than with ATC issues. We experienced delays on every one of the four legs of our flights, sitting for hours without any explanation. Transferring on TAM in GRU is a horrible and chaotic experience, and nobody seems to have a clue what is going on, and the procedures are all very ad hoc.

This is all a pity really, as TAM's on plane service is truly world class and excellent. On board service easily exceeds any US carrier flying to Brazil, and most European ones. Until you get in the air though, things are anything but smooth. It seems that TAM is suffering from the same sort of growing pains as Jet Blue, as their operational skills can't keep pace with the size of the operation itself.

In the future, I'll be reluctantly switching back to U.S. carriers for flights to Brazil.