Ok, I was able to get this going, but it took some doing.
I'm running RaspBMC (xbmc setup for the raspberry pi, built on debian iirc).
hdmi_safe=1 in the config.txt file allowed the monitor plugged into the HDMI>VGA adapter to work during the setup (text based) but after the setup was complete, when the Pi rebooted I lost video.
The Pi would clearly be running, and I was able to SSH in (user: pi password: raspberry) and the shell worked fine. Clearly, then, the pi was working. So, a problem with display!
What worked for me:
Which values are valid for my monitor?
Your HDMI monitor may support only a limited set of formats. To find out which formats are supported, use the following method.
Set the output format to VGA 60Hz (hdmi_group=1 hdmi_mode=1) and boot up the Raspberry Pi
Enter the following command to give a list of CEA supported modes
/opt/vc/bin/tvservice -m CEA
Enter the following command to give a list of DMT supported modes
/opt/vc/bin/tvservice -m DMT
Enter the following command to show your current state
Turns out, hdmi_group=1 and hdmi_mode=1 would allow the Pi to boot up graphically and work fine, but I am currently stuck at a horrendous 640x480. The above commands which show supported modes show that ONLY that mode will work, and my tests have lead to the same result. Other group/mode selections lead to a blank screen.
If there's any way to get other modes working, I'd love to hear it. Being stuck at that resolution makes this largely useless to me, as I was hoping to drive my old LCD monitor (it's dvi input broke years back, but vga works fine - and it takes all manner of resolutions from my desktop over VGA with no issues) at it's native 1680x1050, or at least a standard 720p res.
It's a media center Pi, after all, nobody wants to watch movies at 640x480.