Went out for the evening. Came home and took a peak in to the tank to check on the urchin's progress. I wasn't 100% certain the bare spot in the rock was because of him before. Sure am now. He's only moved about 4 inches since the lights went off at 9, but here's the result (sorry for the crappy night time flash pic):
The bare patch looked exactly like the dark forested patch to the right when I put the urchin in at 4pm. He's not just eating the algae, he's scraping it down to nothing. I can't believe I've never owned one of these guys before. At this rate I'm going to have to supplement him with extra nori soon!