I was one of the lucky folks who had issues with scheduling posts on one of my sites. I found a solution that is different than http://trac.wordpress.org/ticket/3742 and wanted to share, as I believe the issue will continue for a good number of users after 2.7
wp-cron.php uses fopens which is a file operation that looks to act on the siteurl as setup in your site options. When it is invoked, most servers will not recognize that the siteurl is local, and then attempt to go out to the internet, then are directed via dns back to the server.
This self-referential request is disallowed by many more restrictive firewalls. In order to resolve, you need to have your system administrator, host or whoever configure a server rule that will route your requests to your siteurl internally rather than going outside the box.
This is a common problem with operations using fopens, curl, etc.