Basically in real practical terms, I'm interested in how many bits and packets we are pushing over various lines, lans, and interexchanges. I don't really care about what type of bytes they are nor where they are coming from or going to (I kind of care about this, but its a real 3rd or 4th order type of thing).
The data on MAE-East (http://www.mfsdatanet.com/MAE/east.giga.overlay.html) is the type of stuff I'm talking about. I use this daily as a measure of how things are working.
I'm also interested in error counters of various types - to track down and fix broken circuits.
Other stuff I'm interested in is cpu and memory usage on my router and the number of routes and route flap.
While data like how much traffic is tcp or web and length of tcp flows is interesting stuff, my real interest and focus is the switching and: routing capacity of my routers and the usage of my lines.
I'm real interesting in the nuts and bolts of my network and how close to capacity these piece parts are to running out.
One current problem that I am running into is that 32 bit counters wrap too often when the data rate gets high. I would really like to see more 64 bit counters on my routers, specifically bits/sec interface counters.