Warning: Spoilers for Seanan McGuire's Rosemary and Rue and A Local Habitation ahead!
Really, really major spoilers -- as in, I reveal the central mystery of the book and some of the main events!
Ok, that out of the way, here's my quibble (mostly a dangling loose end, not a flaw):
The plot of the novel is that people are being killed by a process that backs them up to disk -- and kills them as a side effect, leaving their blood "empty" (which, of course, is signficiant on a plot level, as it provides an obligatory reason why Toby can't solve the murder in the first ten minutes; something you really need when writing murder mystery novels where the heroine can see through the eyes of murder victims as her primary magical power). Ok, cool.
This process -- of blood being left "empty" due to murder method -- is unprecedented (or nearly so). And we know this, not just because of our heroine's experiences, but because there's a significant side effect of blood being emptied which people -would- notice. One can safely assume there's only one way to drain out someone's personality from their blood, and that's this process.
January -- Sylvester's niece and a large player in the novel, is murdered with an axe, rather than, like most of the victims, without any obvious murder signs.
The villain (the true villain, I should say) reveals, in the denoument, that she deliberately chose to kill January physically rather than "back her up", in a fit of revenge for Jan being noble.
Ok, that's cool, and leads into a plot (and character)-useful betrayal. Except for one thing: January's blood is empty, just like the other victims. This is a big plot element; she even has to have her body burned at the end because Sidhe bodies don't rot. So we know that even though the murderer she said she didn't back January up, she either lied or simplified. If she simplified (she backed Jan up but destroyed the tape; she used the "back someone up" technique but it still works as murder even without media on the other side; whatever), well and good, but it's entirely possible that she lied for effect (with disastrous result...oops) and nobody's gotten around to mentioning to Toby/Sylvester that there's a backup of January somewhere, even if it's a dirty one.
Ok, that said, there are some interesting parallels between the two novels, though they're quite different in other ways:
Main villain is responsible for healing up our heroine before things come to a head (in both cases, the villain has reasons -and- is mad; it's just interesting).
Main villain is motivated by Changeling Rage. Different changeling rage, but still -- is this a series theme? Oh, yeah.
Main villain gets the upper hand during the denouement -- and then blows the engagement by doing something stupid (but very in character) which causes an ambiguous accomplice to switch allegiance at a critical time.