I like how easy it was to set up alerts so we can be notified if our servers are down at any time during business hours (I am in charge).
The interface could use some work but overall this has been very helpful! We have not had an issue with anything as far back from when they first launched until now which includes using them daily since release several months ago - no issues here either!! Highly recommend their products/services. Monitoring my mail system 24x7365 without having anyone there all day everyday would drive me nuts otherwise :).