Mono for Mac Scripting: Rawr!

I take it all back.  In the end, I'm unable to use Mono to script my little project on the Mac, because:

1. I can't wait for processes to complete.  I call System.Diagnostics.Process.Start(myStartInfo).WaitForExit(), but files written by the command-line programs I'm calling aren't on disk by the time I open them for processing in the next step.  I read several places that you need to set UseShellExecute = false to have the process called directly rather than via the "open" command (which returns immediately by default), so I set this property, but it didn't help.
2. The PNG support in libgdiplus is apparently busted.  [Link here when I bother to find the blog post/bug report again.]

Given that this was a project to script the generation of some PNGs with ImageMagick, read them in, and spit out their raw bytes....