If you've been using the .NET Framework since the beginning, you must have had to do some early code profiling, or framerate computation for realtime graphics.
The first idea that pops up to acheive this is to use the DateTime.Now property and do some subtraction of two instances. This is not a good idea since the resolution of this timer is around 10ms or so, which is clearly not enough (and your framerate counter may not go higher than 100 FPS or worse may not work at all).
If you've been in the business for long enough, and been doing some plain old "native" code in, say, C++ on Win32, you should probably used the couple QueryPerformanceFrequency/QueryPerformanceCounter to get the job done. And the same goes for .NET 1.0/1.1. Well, I don't know for you, but each time I have a project that reaches a certain critical size, I always need to use this kind of timer and I end up by writing the P/Invoke wrapper to reach these two methods.
Good news is, .NET 2.0 already has this class integrated in the form of System.Diagnostics.Stopwatch, so you don't have to write it from scratch again and again because you can't find on the net the right "free" class that does enough for you.
The BCL team has added some other nice utility classes like this one, and this saves quite some time.