I can confirm that percentage uniform marks will not be introduced for CIE IGCSE exams for the May/June 2010 exams, however they will start to appear in the Oct/Nov 2010 ones. So on your statement of results, you will only get an alpha grade and no marks.
So I'm guessing that your grade will be determined by grade thresholds rather than by percentiles, as some people have thought.
Some of the countries are being tested for percentage uniform marks, but for the majority, they shall only be implemented from Oct/Nov 2010.
Here is a document I created using the grade thresholds from previous years to determine the A* grade boundary for IGCSE Biology for the previous few years. (Obviously, my calculations are not completely accurate, and they may be a few % off, as CIE do not disclose the A* grade boundaries).
From recent sessions, it seems that 72/73% is enough to get the A*, but my teacher has always said that 80% is a definite A*.
So what will s10's A* grade boundary be? Who knows...