Google maps/earth has a nice mashup tool. But it isn't for private data.
Is there a mashup tool for mapping private data onto Google/Bing/etc maps?
Added It looks like the umapper.com service can be used to import data relatively easily to a mapping system. And they make reference to "private maps" which is what I want. Their import isn't documented yet, I have asked them for more info about it.
umapper apparently works with Bing, Google, and OpenStreetMap. The latter is important since it offers the most liberal licensing for private use. With the others you need to license them for private use ($$$).