Good article, Bjd. The Guelaguetza is a very big deal here, with tickets to the auditorium* sold out well beforehand.
The whole city is filled with people from all over, either tourists, or Oaxaqueños who make a point of coming home for the festival. It seems every other person you see is topped with one of the straw hats given out at the open-to-the-elements auditorium.
The presentations in the auditorium aren't the whole of the Guelaguetza, though. There are side festivals, such as that celebrating mezcal (shown here, where you can also see more of the gorgeous regional dress). There are calendas -- parades with music and giant figures** and wonderfully attired beauties.
There is also a strong political component to the Guelaguetza now, as the faction opposing the present governor has organized a parallel festival ever since 2006, which is free to everyone.
Because of all the rain we've been having, I've missed lots of the activities, but will try to take in something tomorrow.
*Here is a view from the auditorium on the Cerro del Fortín, looking down at the city.
The first auditorium on this site was constructed in 1932, specifically for the first Guelaguetza presentation, in honor of the 400th (post-colonial) anniversary of Oaxaca. More here, if you read Spanish.
Unfortunately, the only information we get in France about Mexico these days is about the drug wars. In the Sunday paper, we were treated once again to such things as "Cartel war spreads to Taxco" and "26,000 killed in drug wars since 2006." They are saying that Calderon is spending too much effort on military operations while ignoring the gun running and money laundering.
I am totally ignorant about this subject, but I suspect that the French press is giving Mexico a hard time because of the Florence Cassez affair.