I have mixed feelings about the FCAT. I took it back when I was in 10th grade and passed it with ease, but I knew of several people who did not pass and had to take the HSCT (we were the last class of students who could graduate with HSCT instead of FCAT). Now, these weren't average remedial students, these were people who had GPA's in the 3.5+ range in the IB program. Personally I don't see how they didn't pass the test, but they didn't.
When I was a junior in HS I left the IB program to do dual enrollment classes at a local community college. Part of this switch meant I had to take a highschool health class with non-IB freshmen. Probably 30% of my time in that health class was spent doing worksheets that "prepped" students for the FCAT. I usually helped the teacher grade the worksheets and was shocked to see that more than 50% of the class was consistently getting EVERY QUESTION WRONG. All of these worksheet questions were very basic (graph analysis, reading comprehension, very basica algebra).
All that being said, I believe that there should be a dual method of graduating. For instance, if you didn't pass the FCAT but had a 3.5 or higher GPA, you would get your diploma. There are people in this world who are never going to be able to pass a standardized test. I don't think it's fair to hold students back based only on a single test, if they are hard workers and have kept a high GPA they should still be able to graduate.