I can help with the Google Earth => Maps

Visit this page, and install 5). This will place a marker in the center of the current view, which you can click on and will open a page that among other things has a link to google maps. [Edit: now opens approximately the same extent!!!]

-> note doesnt work if at a low tilt angle, the center point will be off in the distance

Actully for the other way round, if you view using this map then at the bottom there is a 'Link for the center point' on the map, this again leads to the same page as above, which also includes a link to open in Google Earth. (passing center point only)
[I'll see about adding a link to open direct in google earth]

Hope that helps, Barry