Many sysadmins use Nagios; it's a way of life. I've been using it for over 4 years now and it's a very useful tool for host/service monitoring. The one drawback to it is that when critical notifications hit my phone, a single sound plays regardless of the type or content of the notification. A disk capacity alert or a server outage makes the same noise, which means I need to check my phone in order to actually see what the alert is. If your Nagios installation is noisy because of a very large amount of checked services and not all criticals are in fact actionable alerts, this can be very aggravating.
Since v2.3.5, Gmail on Android can synchronize specific tags to your phone as well as play separate notifications for each tag. Therefore, if you craft a set of Gmail filters to classify your Nagios notifications into categories via tags, you can play a different sound for each alert type.
You can take it a step further by creating mp3 files using this Google Translate URL for each type, then assign it to play for the corresponding tag notification. For example:
Now when you get paged in the middle of the night, you know exactly what's going on, not just that something is wrong.