I'd forgotten I'd tried to set this up once, but I got an update notification today from https://code.google.com/p/google-sites-issues/issues/detail?id=73. The issue is that google sites doesn't support 301 redirects.
How does that effect us? What it means is if you're porting an existing web site to google sites, you're about guaranteed to have things break. If anyone's linked to an index.html page of yours, or default.htm, you're stuck with a 404 report forever. You can't even load a blank page with an embedded redirect because google sites changes the document type so your browser won't read it correctly.
The funny thing is google likes 301 redirects. They even made a video to show you how cool they are. But since it's been a year since good old issue #73 was logged and there's no update, my guess is google sites will just never support this feature. Which probably means google's going to abandon the product.
I can't imagine anyone recommending moving an existing site to google sites, or even starting a new one from scratch with it.