The latest release of the Google Mashup Editor lets your mashups share data between users, letting you create real social apps within the GME. So My Travel Maps now includes 'Their Travel Maps', a tab where you can see your friends' Travel Maps.
Sign in and add your friends' GMail addresses to the 'Their Travel Maps' tab, then select a friend to see their trips (and their Picasaweb albums). Add me as a friend -- my GMail is Reto.Meier at gmail.com -- to see the result.
Along with social application support this release has a bunch of new features, including the ability to add labels and rating to external feeds, support for editing HTML and CSS project files within the editor, plus better styling and CSS support along with general performance improvements and bug fixes.
It's an impressive new release that's moving the GME further along the path to full-blown online GoogleOS development IDE.