As this blog post describes:
...I find the performance monitor graph highly useful. But I would like to add simple custom counters to this, it is possible?
In our particular case we're running a lot of different tasks in parallel, and a counter for how many things are currently executing in parallel would be very useful when troubleshooting performance bottlenecks with builds. I suppose this could either be implemented using teamcity's "service messages", or maybe some naming convention of windows performance counters (teamcity*), or even by writing directly to the statistics database (it might already be supported, inofficially?).