I've read a few posts with cron issues, but this feels different.
I upgraded to 2.7, and everything was fine. My web host then switched their load balancing to use squid as a reverse proxy.
After that, scheduled posts no longer posted, pings no longer get sent out. I installed wp-crontrol and core-control. Through a process of elimination I found that cURL wasn't working. My web host found an issue with their networking and corrected it, so that now cURL does work.
However, cron still doesn't work within WordPress. If I manually execute wp-cron.php?check=<correct hash> then it processes all the outstanding tasks, but if I just leave the site alone, jobs turn up in the cron queue but never get actioned (it certainly gets enough hits) and eventually schedule posts get marked as missed.
I'm out of ideas. Any help appreciated!