Some web sites put "autocomplete=no" in their login forms to prevent your web browser from saving your password. I find that annoying (if I've told it to save my passwords, then I'd like my passwords saved, thanks) so here's how you fix Safari so that it will treat those forms just like all the others.
sudo sh cd /System/Library/Frameworks/WebKit.framework/Versions/A/Frameworks/WebCore.framework/Versions/A/ mv WebCore WebCore.orig perl -pe 's/(\000)a(utocomplete\000)/\1_\2/gsi' < WebCore.orig > WebCore
Then re-launch Safari.
This change will get blown away the next time Software Update sends down a new Safari.