This one is worth repeating:

Quantum effects in microtubules are going to be inconsequential relative to ion fluxes and chemical changes in membrane properties and channels, and there is no explained mechanism to regulate quantum effects. It’s like trying to explain the tides by speculating about the dabbling of gnats in estuaries.

The people who talk about this stuff usually seem to have absolutely no knowledge of neuroscience.

For sheer disdain, this might be second only to Patricia S. Churchland‘s remark, “The want of directly relevant data is frustrating enough, but the explanatory vacuum is catastrophic. Pixie dust in the synapses is about as explanatorily powerful as quantum coherence in the microtubules.”

My most extensive essay on this subject can be found here, and a good paper with many references into the literature is A. Litt et al., “Is the Brain a Quantum Computer?” (Cognitive Science, 2006).