The Boxoffice Mojo site seems to follow the takings of movies around the world, so if you want to keep track of how TF3 is doing, head on over to this site and have a browse through the options.

As of its first two weeks, it has generated over US$700million worldwide... a lot more than its budget (which is said to be US$195million, according to imdb.com). I think that guarantees another one.

In its first US weekend, the three TF movies raked in:
$70million - TF1
$109million - TF2
$116million - TF3 (and had a smaller decline in the second weekend, than TF2, which means it is holding audiences longer)

And worldwide in just its first two weeks, TF3 has already earnt as much as TF1's total earnings of about $700million.