i agree on the perceived brightness.
i dont know why, as Andrew said it's the same white background as before? maybe there's less other stuff going on on the screen than before to block the whiteness a bit or to box of the screen a tad?
I noticed instantly. being dyslexic reading black text on white is difficult, i have a program which adds a colour over the screen though, which i have had to start using with the site now.
when i lift both hands in front of my face so that they cover both sides of the screen, it becomes much easyer... maybe making the area on the left and right hand sides, the bits outside of the grey box, a darker colour/shade would make it easier to read what's in the centre of the screen. just an idea