I've seen this happen twice now, but it doesn't happen every time: 1. Move aside your Databases directory (on XP, it's C:\Documents and Settings\username\Local Settings\Application Data\Apple Computer\Safari\Databases) 2. Go to <http://webkit.org/demos/sticky-notes/index.html> An alert appears that says "Couldn't open the database. Please try with a WebKit nightly with this feature enabled".
Looking at the source for the page, this either means that "window.openDatabase" evaluated to false/undefined, or that calling openDatabase threw an exception.
<rdar://problem/8014859>