Why not just get the events directly and forget the MoM? If a management system is implemented to oversee a specific domain, say Microsoft Windows NT or database servers, or routers and switches, this plan makes more sense than forklifting what's in place. Different portions of an IT organization have the responsibility for managing these various systems.
On the other hand, while separate management domains offer useful and granular performance information, they lack perspective on how their performance affects other devices in the chain. Without event correlation, it's impossible to deduce that a faltering switch is causing long application-response time. The MoM's job is to bridge the event streams of various management domains by monitoring all pieces of the business IT services. Conversely, it is not the role of the MoM to provide granular diagnostic and tuning data on how a database, Web server or network switch is performing.
Today's MoMs have a more difficult task than previous generations did. Multitiered applications run on separate, distinct systems, forcing the MoMs to gather and correlate a wider array of events.
Earlier MoMs had the advantage in that transactions, application logic and databases all lived in a single monolithic mini or mainframe computer. Matrons such as the earliest versions of BMC Software's Patrol Enterprise Manager have provided event management and automation for Fortune 500 companies and service providers since the 1980s. These products focused disparate enterprise and system problems onto a single pane of glass, and gathered data from as many sources as possible--other management systems, performance point products and even devices with only proprietary serial interfaces, such as air conditioners and security systems. The value beyond having a single point of management was a reduction in the number of events, through deduplication and visual correlation.
MoM vendors Aprisma, BMC, Managed Objects, Micromuse and System Management Arts (Smarts) point to the improvements they have made, such as root-cause efficiencies aided by discovering Layer 2 topologies and using object-oriented data models. Still, this category remains complex. You won't move from crumpling the cellophane to managing multitiered, networked business applications in a day, though if you don't expect miracles out of the box, implementation and project planning will improve, and you'll likely contain costs along the way.