Multivendor networks exist everywhere. Servers, backup systems and a seemingly endless list of elements all have their role in, and view of, the network. More than ever, prudent network designers should care about the extent of multivendor and that it actually exists in solutions they are considering.
As Linux has started nipping at the heels of Windows in recent years, Microsoft has admirably launched an ongoing effort to quantify the total cost of ownership of its offerings vs. alternatives that are mostly on the server front and mostly the aforementioned Linux rather than, say, Apple OS X or Sun Solaris.