Aww that's a bummer...
Id have thought the renderer would have been multi-threaded. it would still work on a single core 98 box since the OS takes care of threads and which core to run them on.
My idea of multi-threading the renderer would be to divide the render-view into a grid and each grid-square render on a separate thread.
For each grid as soon as 1 pixel gets a colour, fill the square with that colour, repeat for each corner of the square then divide up the square into 4 rendered pixels etc., etc. until the frame is fully rendered (or stopped).
You could set a menu option for the number of grids. (thereby limiting the number of threads to a user amount for large images)
It would be up to the user to choose either (in my case) 16 threads, each logical processor would run at 100%, or use more for a finer grid but incur OS latency in thread switching.