Pretty useful Unix/Linux (see also: GrepPlantation) command, lets you do things automaticaly at set times, bastard if you fuck it up.
Recovering a crontab using logs
If you overwrite your crontab, haven't got backups (AlwaysUseBackups) you'll have to look at your logs to find out how to patch together your crontab.
Here is a quick guide on how to do it. Maybe it could be converted into a quick script.
Next get a list of the commands that appear in this section belonging to the user whose crontab was nuked. In my example I use 'root' change this as neccesary. I'm assuming you have the standard GNU grep. I am grepping the actual cron log however you could copy this and remove older irrelavant entries.
grep -B1 '> root' /var/cron/log | grep CMD | sed 's/> CMD: //' | sort | uniq
This will give you a listing of every command appearing in the log.
Next you need to find the regularity of these commands in order to regenerate the crontab.
So for each of the commands you wish to recover do the following.
grep -A1 'logadm' /var/cron/log | grep root | tail -30
This will show the times at which logadm was run the last 30 times which should be enough to figure out the pattern with which it was run.
The rest should be easy.