After installing vixie-cron-4.1-80.fc7, "crontab -l" or "sudo crontab -l" or "sudo crontab -l -u $LOGNAME" claim that there no crontab (for me, root and me, respectively). There are, in fact, crontab files, and crond is merrily running the commands in them. I have selinux disabled; I don't know whether this is relevant.
Copying the crontab files out of /var/spool/cron and running "crontab <file>" on them fixes the problem -- after doing that, crontab -l can see them.
After doing the step described above, I've got two crontab files, one in /etc/cron.d and one in /var/spool/cron, and both are active, which means that my jobs are being run twice. Something definitely needs to be done about this.
The man page doesn't mention /etc/cron.d at all. And, as noted in another bug report, there are files in /etc/cron.d installed by packages like spamassassin, so it doesn't make sense that crontab is putting files in this folder. There's something here that definitely isn't quite ready for prime time.
Fixed in vixie-cron-4.1-82.fc7
How was it fixed? Putting the files back in /var/spool/cron where they should have stayed, or fixing the /etc/cron.d behavior? If the latter, then what about other RPMs that put files in /etc/cron.d? And has the man page been updated to mention /etc/cron.d?