In response, noitaminA Editor-in-Chief Kouji Yamamoto-- who says he wrote the script for the episode --tweeted an apology to the staff of the series for the low ratings. (Via MAL.)
That said, I think there's another explanation: the noitaminA slot just opened up to being an hour instead of 30 minutes, and House of Five Leaves is in the new, later (1:15am) timeslot, while next week's The Tatami Galaxy (also to be simulcast by FUNimation) is running at the more familiar 12:45am slot. It may just be that people aren't aware of the change yet.
That said, I think it's a pretty good show. But hey, maybe we can do a thing or two about it! FUNimation already has the first episode on Hulu, which means we can embed it. So here: if you're in the US and haven't already watched the first ep, take 25 minutes and do it now. If you like the episode, just pass on the link to a friend (or, if you feel like being an overachiever, send it to two). Let's see if we can get the show more popular in the US than in Japan! (...Okay, maybe not, but hey, we can at least spread a good show around.)