Mouse - I recently met a nurse who suffers from normal pressure glaucoma which is not so slowly making her blind (hers is not reversible by lowering intra-ocular pressure); we were discussing increasing circulation to the optic nerve and I mentioned gingko. She said that she wouldn't take it because it's been shown to increase the chances of retinal bleeding. So if you're susceptible, you might want to research that before taking gingko. I've been taking it since before my last high-altitude trip in August (thought it might help my cold hands and feet in winter) but you just reminded me to go Google the bleed thing.

P.S. I just googled and found that gingko decreases platelet aggregation (which would slow clotting), and that it has been associated with a few cases of retinal bleeding when used in conjunction with anticoagulant therapy. I imagine that if you had any sort of hereditary clotting factor deficiency, it might also be a risk.