Is there some scale (energy, length, and time) on which the linear superposition principle breaks down?
Is the quantum-classical "transition" a crossover or a phase transition?
What are the distinct signatures of quantum complexity?
Which interpretations of quantum theory are not experimentally falsifiable?
Are there any biological processes which require/involve quantum coherence beyond the nanometer length scale and picosecond time scale?
Are there any experiments which should cause one to abandon a philosophical position of critical realism?
Why doesn't the decoherence interpretation solve the quantum measurement "problem"?
In what sense can the classical world be considered to be an emergent phenomena?
Hopefully, I will write more about some of these soon. Comments and suggestions welcome.