In Safari 3, you could use the Up Arrow key to get to the front of the Google search field (while entering search terms) if you wanted to add quotation marks, or make other changes. With Safari 4 Beta's new Google Suggestions feature, this editing trick stopped working. However, you can use Command-Up Arrow instead, which will mimic the Safari 3 behavior.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090331205623866