What are the criteria for successful network performance management?
To do it right, you need to accomplish the client's goals. The client's network must perform at the level they need for the price they're willing to spend. There are obviously practical limitations to what you're able to do as a solution provider. For example, you can't make a DSL line go faster, but you can manage the bandwidth available on it, so you can potentially provide a modest apparent improvement. So if the client can only afford a DSL line, and you can make that line perform as well as it can, that's a successful project.
That scenario is quite different from one where the client can afford substantial bandwidth, but wants to ensure that certain applications meet particular performance levels. A common example is Web page rendering speed. A client may require that the Web pages they serve are fully rendered in five to seven seconds. The point is to understand the client's criteria for success before you attempt to deliver the solution.
It's important to note that there are often no set performance metrics to establish the success or failure of a project. You're essentially creating those metrics for the particular client -- you're figuring out which metrics are relevant to the client's goal. The client may want their network to run fast, but you need to define what "fast" means.