There are many sceptical voices across the web already. And honestly, I also have quite a bad feeling. At the moment of ET separation I will be more than just glad. Did they find all cracks? What if there are another cracks? The External Tank absorbs the tremendous vibrations from both SRB's. Imagine if cracks are causing a part of the ET structure to fail, which I think is more likely than unlikely. Would be interesting to know what the Lockheed Martin guys in Michoud are thinking about it...
The only cracks that have been found so far are in the stringer area (intertank). These cracks could lead to foam liberation. If foam is liberated at certain section of the ET it could hit the shuttle during ascent. That is the only fear.
None of the engineers ever questioned the structural integrity of the tank in all. In fact they consider it -based on the gathered strain gage data from the last tanking test- even stronger than needed.
I think it is not helpful to stoke fears about a possibly failing ET stucture due to any cracks. The cracks are located at the upper end of the stringers only and they put doublers on it now. No astronaut would enter the shuttle for lift off if he would have any doubts about the repaired ET.
We should not support any rumours of people that are eager to spread their (often unprofessional) view or fears through the internet.
This is all I have to say.