@sgw I had exactly the same thing happen to me. GUI would not start but the device functioned correctly.
I left it alone, ordered another SG-1100 and installed it, then reflashed the original one. So now I have a hot spare ready to go should I need it.
As far as not waiting long enough, mine (updated via the GUI) sat for a long time on waiting for the GUI to reload, which it never did. That's why I power cycled it. Would it eventually have come up? Don't know.
Anyhow, now I'm really gunshy about attempting another update, especially with all of the users reporting problems. I'm content to leave that green light flashing.