Via Ogle Earth, a new way for two people to share and show positions in Google Earth, GE Sharing. Unlike Unype, which requires a Windows-only download, this uses a shared network link, making it cross-platform. Site is in German, but if you click on the “Los geht’s!” (“Let’s go!”) button, and follow Stefan’s English description at Ogle Earth, it should be pretty straightforward.
Addendum: Here’s the link to the English version of the page.