There was a really good discussion at the conference which clarified a few things for me.
Just how quantum are the effects (interference of excitons) that have been observed?
John Briggs asked how this was different from coupled harmonic oscillators?
Where does h-bar enter?
Shaul Mukamel pointed out that as long as one is looking in the one exciton sector the Heisenberg equations of motion just look like classical harmonic oscillators. hbar only enters as omega=frequency=E/hbar.
This is just like how the Bloch equations can be viewed as equations for a damped harmonic oscillator.
These questions about true quantum effects are reminiscent of the birth of quantum optics. People thought photons were necessary to explain spectroscopy. But actually this could all be explained in a semi-classical framework. It was only with experiments such as photon anti-bunching and squeezing that the truely quantum nature of light was established.
To see true quantum effects such as entanglement one will need to look in the two-exciton sector. Then a definitive signature of entanglement would be violation of Bell inequalities. Until such an experiment has been performed I see no justification for making claims that entanglement does exist in photosynthetic light harvesting systems.
Extra-ordinary claims require extra-ordinary evidence.