I have found that it can be really annoying trying to get Google Gears to work with Safari. I was able, eventually, to get Google Gears version 0.5.15.0 to work nicely in Safari 4 beta. The install and update process, however, is somewhat of a mess. I had Gears installed with Safari 3, and found that I had to manually remove it first by running this command in Terminal:
/Library/Internet Plug-Ins/Gears.plugin/Contents/Resources/uninstall.command
After uninstalling, then you can go back to the install page and re-install the latest version for Safari 4 Beta. Now enjoy offline Gmail, Gcal, and Google Reader in Safari 4 Beta. I don't know if this version works in Safari 3 though ... does anybody else know? Please chime in below.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090303073242222