I really didn't mean to take so long to list this. I actually left it at work, and read it slowly whenever I felt like it. It's relatively easy to read, and the story is also fairly interesting. Obviously, it doesn't contain a gripping story, as this series is all about calm, cute, heartwarming, and occasionally strange events.
Hiro is too simplistic as a character. Everybody pokes fun at her "diet" and her occasional motherly behavior, but there's rarely more to it. Sae is actually a lot more interesting because she is in fact a professional writer. Miyako is obviously the main ingredient, though, with Yuno keeping everything together.
First part of the book overlaps with the original manga. It talks about Yuno moving to Hidamari-sou and meeting all the strange neighbors. Last part is an original story in which Yuno has to take care of the landlord's sister's son for a couple of days, or something like that. I forgot the actual relation. It's not important anyway. Basically, Miyako takes the lead and brings out the best from the boy, with help of all the Hidamari-sou residents.
I would like a CD drama from this story, especially the place where Yuno is imagining all kinds of stuff Miyako is saying.