I think the 'final word' (well, as of this moment in time) on the deterioration of reusing bottles was what they were exposed to.

If they contained or were cleaned with harsh chemicals that degraded the inner surface of the bottles, leaching problems could result.

And if they are exposed to sunlight, deterioration also happens, esp due to the UV exposure.

But normal, clean bottles of the clear type, which have more tensile strength than the milky ones, are fine for use and reuse.

For instance: http://www.snopes.com/medical/toxins/petbottles.asp

Sue