I would like to report an issue in WordPress 3.
I was facing the same problem where ‘Screen Options’ menu tab was not visible on the admin dashboard.
I carried out some diagnosis on the PHP code and found that WordPress 3 requires 256Mb of free memory to be available on your web hosting package.
I found two places where this memory limit is being set:
wp-admin/admin.php
wp-admin/includes/file.php
I commented out the code snippets in both of these places and this sorted out the problem.
Because the code was not completely executed, the ‘Screen Options’ tab did not appear, also therefore, there was no ‘Publish’ button visible while adding a new post or a new page.
I would suggest that WordPress Software kindly include a message while installation or upgrade of WP version 3 to notify the administrator that this amount of memory is required to be free on web hosting otherwise there will be issues.
I hope this helps!
Sumeet.