This will most certainly be interesting to watch. My visceral reaction to the idea of one giant room was, "Wow. No thanks." I'm not personally the biggest fan of Frank Gehry's work, either. That said, I'm always a little bit excited when people push architectural boundaries, especially when it comes to workspaces. Hopefully my friends at Facebook will still be around when this is completed.
My visceral reaction to the idea of one giant room was "Rad". Love open floor plans. I'm really curious what the final interior plan will look like; presumably it's not some huge airplane hanger of openness but some clever way of staying open-while-interesting. Like you, though, I'm just excited at the prospect of larger companies doing something different. Should be fun to watch.
I'll reserve final judgement until it's built and we can see pictures/video.