WCF Syndication APIs are great. In just a couple of hours I wrote a simple GeoRSS feed, a fairly high level library to encapsulate the details of common entities (lines, points, polygons), all unit tests and a mashup with VE to test it.
I only encountered a couple of incompatibilities and problems (mainly related to XML namespaces) but everything was straight forward and easy. VE doesn't allow the RSS feed to come from a different server the map is hosted, so you need a proxy to walk around this limitation (Very well explained in this blog entry. A must read for anyone doing VE stuff. Thanks for the code!).
Being fairly new to this is space, I was amazed at the power off all these infrastructure components, and the apps that could be built with this stuff; and I know I have just barely scratched the surface.
My library allows me to easily author a GeoRss feed:
GeoRssData is a simple object model for geo information. GeoRSSFeedBuilder translates the domain model into a RSS feed with the proper extensions. This is all quite easy with WCF Syndication classes. Finally this the result on IE: