So, Apple turned at off by default, cause who uses at, right? Well, I do. Here’s how you can too:

$ sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.atrun.plist

Once this is done, the at service is running. To make a handy-dandy alert system, try using at with the “open”OmmWriter in Action command, like so:

$ at 3:01 today [hit return]
ps ax | open -f [hit return and Ctrl+D]
job 9 at Wed Mar 10 03:01:00 2010

This will run the ps command and pipe the output to the open command. The -f flag tells open to place the input into the default editor for the system, so when your at job runs, TextEdit opens with your ps output.
Also handy for things like:

$ echo "STOP WORKING and go home, you loser" > /tmp/opentxt &&
open -W -a OmmWriter /tmp/opentxt &&
rm /tmp/opentxt

This will clear the screen and tell you to go home. :)

So, here I go.

/cs