Here is an interesting post on Avandia. It points out the discrepancy between the number need to treat (to show benefits on the key endpoints) and the number needed to harm (with a myocardial endpoint). Now, the author is neglecting the uncertainty in these two numbers.
But it's a pretty clear that if the number needed to harm is 50 and the number needed to treat to prevent a serious outcome is 1000 then the medication is likely not favorable on the cost-benefit analysis.
There are cases where the risk-benefit calculation is a subtle problem and it is always tricky to withdraw a drug that showed actual benefits in the original clinical trials. But it is looking increasingly like Avandia may carry more risks than benefits making it an exception to the rule.