Great apartment, great neighborhood, great host. Daisuke sent a really nice guide of things to explore (we tried some, they were accurate), and offered to meet, sent suggestions, and even offered to help with suggestion for things to do in Tokyo after our stay. Apartment is very stylish, the size should be ok for two people (even using the sofa bed like our case). I actually forgot to mention I was going with a friend (and Daisuke was pretty nice to accommodate it, there were extra sheets/covers), so when extending the sofa bed (and under it) was a bit dirty, but everything else was sparkling clean. Bathroom is just ok though.
Shimo-kitazawa is a pretty cool neighborhood, pretty fun to explore by foot. Go check the Totoro cafe! Apartment is really close to the station, and the train goes to Shibuya (make sure to get the express one, then it will be non-stop, it just takes a few mins), it's subway so it won't be included in your Rails pass.
A bit on the expensive side, but we had a really good time, recommend it.