That's always been the theory, but it's good to be cautious. The upgrade from Sarge to Etch was a bear for some people because of the XFree86 to Xorg conversion. Now is the time to do the conversion. Beat the rush.
Replacing aptitude first as demonstrated in the article is a very good idea. If you encounter an error during the "full-upgrade," and there are several common ones being reported; remove/purge the application causing the error, then "aptitude install -f"