The article seems to say that only about a quarter of the students graduating in 2008 and eligible for the Pittsburgh Promise actually used it, since some students go to school out of state and some do not go on to school at all. There doesn't seem to be any information on whether a higher percentage of students from the class of 2008 went on to school compared to previous graduating classes.
There is also a split concept mentioned, which seems to be new. Students who cannot meet the increased GPA requirements receive the amount of Promise money that was available under the old GPA requirements. Previously, the idea seemed to be that all Promise money would be subject to the new GPA requirements.