I had an amazing time staying with my girlfriend at Daisuke's place in Shimokitazawa. Not only is it in a great neighborhood to begin with, but he has the scoop on the greatest places around (seriously, follow his advice, you won't be disappointed!). The apartment was super clean when we came in, he provided very thorough instructions for getting to the place and how to be a good guest, and was very responsive whenever we had a question. Do follow his advice and download or print his instructions so you have them at hand even if you don't have roaming data on your phone--you'll thank me later.
All in all, to my mind Daisuke's listing represents some of the best that Airbnb has to offer. Would absolutely try to book a stay at Daisuke's place again if I'm ever back in Tokyo.
I imagine that it would be a tight fit for three or more people, but it wouldn't be so bad if it's just for a night or two. For two people, it's just the right amount of room for you to be comfortable.