If the web inspector is open before a page is loaded, the console does not display Javascript parsing errors. Closing the inspector window and then reopening it workaround and displays errors. This is both on Safari 3.1 and Webkit nightly, 10.5.2
Confirmed on Safari 3.1 on Windows XP.
To test: 1. Open a new window 2. Open the Web Inspector 3. Go to data:text/html,<script>}</script> Results: There is a red bubble next to the main resource with the number "1" in it. This is correct and expected. The problem is that beneath the Console icon/text should be the text "1 error", and when you click on the Console you should see the error message "SyntaxError: Parse error"
Not sure I'm entitled, as the reporter, to do that, but this issue is resolved for long now. So I update it as fixed