I did finally figure out something that works, although it's probably not “right” at all! In fact, the epub validator doesn't approve it, but Kindlegen does. I, too, couldn't get any of the other suggestions to work, even though I tried 1) adding “start” into the guide as described above, and 2) only including three “types” in the guide (cover, toc, and text) which was suggested on a blog I read. Anyhow, here's the workaround I use, and this seems to work fine:

You've already noticed that the Kindle opens your book at the start of the LAST page rather than the first page. At the end of the line in the guide for the last page, remove the phrase type=”text”. Then remove that same phrase from all the lines above it EXCEPT for the first one (where you want your book to open). Voila. This will show up as an error message in all validators, however it does seem to work just fine and KindleGen will still congratulate you.

I would love to learn of a way to do this that doesn't produce error messages, but so far have had zero luck. I hope this helps!