I use it to monitor my RS/6000 systems and it checks the following;
Connectivity
CPU - load factor, number of users, number of processses, uptime
Disk - filesystem usage
Msgs - error log entries
Oracle - Database processes
Listener Status
Check Alert Log for Errors
Check Backup log for Errors
Check number of indexes is correct
Check free space in database tablespaces
All is configurable - e.g you can have Oracle partitions 100% full with no warnings
Some of this is default, some from scripts on the ftp site
I don't use it to alert me as we have 24x7 users that do that
There are scripts available to send messages to pagers, txt to phones or even html to WAP phones
The choice is yours !
Alex