I use this solution regularly for analyzing incidents, collecting them to figure out what's going on. For now, I'm using it myself but would like to also deploy for some of my customers in the near future. I'm an entrepreneur in a security solutions company and a customer of Graylog.
Our primary use case of this solution is for logging. Because we have financial systems, we also use it for audit trailing. I basically run the entire program in our company. Whenever there's an audit, I get the people on board and give them the information they require.