Splunk has give us the capability to easily track problems and their status. Our security operations team has been able to use it to track where people login and what they do on those machines.
Personally, I like the capability of removing sensitive data before it goes into Splunk. I also like the ease with which dashboards can be created.
I like Splunk. The only thing which can be improved is that they are too subjective on whom their Splunk4Good initiative can be applied. They market it as you only need to be a nonprofit, but there is more to it.