Safari 4 Beta
Apple has released a beta of Safari 4 for testing purposes. If you install the beta be aware that many apps rely on the underlying webkit engine that powers Safari and they may break. Of note: growl with the GrowlMail add-on no longer works after installing Safari 4 beta.
Also I can't find it documented anywhere, but access keys now require you to press control-option(alt) in the Mac version of Safari 4. For an example go to UM Wiki and press control-option-p to see a PDF of the front page. In previous versions of Safari for Mac you would just press control-p.