Great DL (do get a vid filmed from the side sometime though, impossible to tell what your lower back area is doing there)!
No good on the squat. I'd suggest contacting maraudermeat... His posts have helped my squatting technique a lot.
One big problem you have is that you aren't really setting up before the lift... Remember your cues, tight lower and upper arch, big air/tight midsection etcetc.
The way you are squatting now it looks like you really aren't even getting tight at the beginning, so it's no wonder that you completely lose your arch (didn't really have any to start with though) and sort of cave in on yourself going down.
You need to be fully set up and tight before you even consider going down.