A big, huge thank you to everyone who commented and weighed in on the question of graining + riding. Consensus seems to be that it really won't hurt either way, but most of us wait anyway. I'm glad I'm not too much of an outlier.
A commenter also pointed to the existence of another blog post giving some of the great scientific background to the conversation, from Team Flying Solo, which I have to apologize out; it actually sparked my thinking on the topic and led to my post, but I failed to acknowledge its existence.
So here, go and read and get some more background: Rocket Fuel & Other Stories