Oooh I've read them!
I had my doubts about Cassie Clare at first (the whole Draco trilogy plagarism scandal) but I do enjoy these books.
SPOILERS...
On the subject of Twilight, uhh no. I don't like Twilight and so the almost Buffy-esque series with a strong female protagonist was really a breath of fresh air. I'm happy with the series, and I was quite impressed with how the writing style progressed by City of Glass, though I do have to admit that it got pretty predictable at times. ("Sebastian," anyone?)
Speaking of ol' Sebastian, and your musing about the lack of backlash, I think mostly people were so accepting of the Jace/Clary relationship because there was so much forshadowing that they were not actually brother and sister. It was obvious from Luke's story in City of Bones, when he talked about Jonathan's white-blond hair (Jace's is described as golden), and from all of Clary's angsts about how little Jace looked like her family. When Valentine talked about making a monster, and when we learned the truth about the Inquisitor's son, there was just too much evidence for them to be siblings. By the time we got to the familiarity of Clary and Sebastian, most of us had already come up with theories about who Jace really was and why Sebastian was the real Jonathan. Similarly, despite their feelings for eachother, both Clary and Jace tried to stay away and make it work. When Edward and Bella did that, both of them went catatonic for six months and then tried to commit suicide. *Okay, no Twilight-bashing. Breathe.*
Back on topic, you might be a little suprised to know the huge critisism Cassie received from the Wayland Manor scene in City of Glass. A lot of fans were very disgusted by that scene, some even claiming to throw the book across the room or feel like throwing up. Personally, I didn't mind it because I actually kind of wanted them to be brother and sister, but it was a big turnoff for a lot of people because they couldn't see the characters making out like that while they still believed they were siblings.
A little off-topic... Are either of you going to the party in NYC this Saturday? I live only a few states away so I can probably make it. It sounds like fun...