Suffice it to say that the matter is currently being studied and evaluated by TSA - it is very possible that the defective Sony batteries found in some Dell laptops may not be allowed. Everything points to a manufacturing defect in the Li-ion cells used - small metal fragments that can cause a direct short when used.
So, rather than leaping in place, just wait and see how it plays out.
In the meantime, check this site for the latest requirements.
TSA