We just returned from our 1/24-1/31/11 trip.
The Brazilian tour groups definitely added to the crowd levels at the parks. The groups can quickly congest an area of a park, similar to the migration of the Wildebeest.

Strategies to deal with their impact:
1) Avoid the park with PM EMH
2) Stay ahead of the flag-bearers
3) Do not follow the groups into a line queue
4) Play capture the flag and lead the groups to another side of the park.
5) DHS will be crazy on Fantasmic nights, go to DHS on a different day. Both the 1st and 2nd shows were packed.

Overall, crowd levels were not bad, ranging from walk-on to longer than posted wait times.