I had a problem last night where I wrote a post, gave it a date to be published in the future and had it promptly disappear on me. Granted, I'm using an older version of WordPress (2.1.3 until I can test the latest release), but I certainly wouldn't expect functionality to stop working. I ended up having to do a bit of database digging to bring it back and thought it might not be a bad idea to share what I found and how I fixed it.
First things first, I did a search to see if the post was in the database. Sure enough, I located it, but several of the settings were all screwy. The post_date was set to a default value of 0000-00-00 00:00:00 instead of the date I intended to publish. The post_date_gmt field had the correct time, month and day, but for 26 years ago. The post_status was also set to publish instead of future. I can't figure out what would have caused this strange error, but updating those fields through the mysql command line caused the post to appear in WordPress again as a scheduled post. Go figure.