I leave for a few days and come back to... this topic of discussion. xD I haven't read through everything I've missed because there are way too many pages, but I'll post my opinions on the topics I saw while browsing through.
I think the turian collar is part of their body, but the armor really does exaggerate it. I would guess that it's closer to the size shown in Garrus' casual outfit. There was one screenshot of a turian a few pages back (the one in the cute hat) who doesn't seem to be missing the front piece of the collar though. So now I'm guessing that it varies, like fringe shape and length. As for biological purpose, the best one I've come up with is radiation protection for their neck. Their skin is more exposed on their necks than anywhere else, and having metal plates on the necks themselves would restrict movement, which means... collars, the next best thing?
I didn't know that Saren was originally planned to be the only turian in-game, that they hadn't planned them as a species. Turians are the best-designed alien race I've ever seen, and it all started because of Saren? Now I have yet another reason for him to be my favorite.

Okay guys, this last part of my post might involve minor
SPOILERS as a response to the conversation that went on for several pages about squadmate x squadmate relationships, but nothing that hasn't been said already.
I've never supported pairings between squadmates. When you imagine your many Shepards on-board the Normandy together, as I do, then it just gets plain
weird to see a squadmate romancing someone who is not the Shepard you've paired them with. It's like they're cheating on Shepard, even though that Shepard technically doesn't exist in other playthroughs. I have a lot of Shepards planned of both genders, and the Garrus/Tali romance will be showing up in many of those playthroughs.
On the bright side, if I had to choose one character besides Shepard for Garrus, it would be Tali. I consider her a close friend as well (even though not all of my Shepards feel this way, it is a vast majority). Tali's my favorite female character. If Garrus ended up with Liara or Ashley, who I've never liked at all, I would naturally be much more opposed to the idea. I can get used to the idea of Garrus and Tali together... and try to ignore it a bit, I suppose. Again, trying to look on the bright side, maybe this will help make it easier for me to play other FemSheps who romance Garrus without feeling like he's cheating on the other one.
Any other big topics I missed? Oh yeah, the art book. I've got to get that sometime.