gmaps2kml is a simple site that does exactly what it promises: Turn your view inside Google Maps into a KML placemark ready for Google Earth.
(Recap: Another option is this KML generator. If all you want to do is switch views from Google Maps to Google Earth, I recommend MutantMaps for Firefox browsers. There is also a manual converter between the two.)
[Update 2005-08-01, 10:27 UTC: Please note a comment left by Earthhopper, who thankfully speaks Japanese, and who thus was able to understand that, in addition to the page above, there is also a bookmarklet that can be used with Google Maps to put a placemark in Google Earth. The great thing is that this works with most browsers, not just Firefox. So read the comments.]