Just ran into a similar issue on my laptop, which is a Toshiba Satellite A505-S6960 running Intel graphics. In that case, I at least got a wallpaper and mouse cursor, but still no visible windows until I did a unity --replace. That brought up a visible terminal window without decorations and stuck in the upper-left corner, and produced a crash (Bug #932125). Since I couldn't get past Firefox back to my terminal, I did a Ctrl+Alt+F1, logged into a tty and ran unity --reset there, which also fixed the issue on my laptop.
From what I've seen on my machines and from what I've heard in IRC, this issue is graphics-independent.
Just ran into a similar issue on my laptop, which is a Toshiba Satellite A505-S6960 running Intel graphics. In that case, I at least got a wallpaper and mouse cursor, but still no visible windows until I did a unity --replace. That brought up a visible terminal window without decorations and stuck in the upper-left corner, and produced a crash (Bug #932125). Since I couldn't get past Firefox back to my terminal, I did a Ctrl+Alt+F1, logged into a tty and ran unity --reset there, which also fixed the issue on my laptop.
From what I've seen on my machines and from what I've heard in IRC, this issue is graphics- independent.