If you using the personal blogs, then this makes it pretty easy.
The /people/<username> pattern is universal. If you can grab the URL and parse out the <username> (making sure to unencode it), you should be able to use it with the
service to get to the user.
Other than that, there aren't any services that turn a URL into it's API equivalent. The closest you would have, would be to get the contentType/contentID and use the
to return the Place/Content.
Hope that helps,