IronPython is to .Net/Mono what Jython is to Java. That's the simple way of saying things. The reality is that IronPython is a remarkable software and if it is good, then it is due to the talent of it's creator Jim Hugunin.
Jim Hugunin has presented a paper on IronPython at PyCon 2004. The benchmarks are amazing - IronPython runs on the JIT compiler of .Net faster than on the CPython native executable written in C!
Miguel de Icaza must be a very happy man to note that IronPython has proved that .Net is indeed usable with interpreted languages.
The combination of Python and .Net is very compelling indeed. The advantage is that you get to write powerful Python programs using the excellent .Net libraries. I cannot imagine anything more awesome than this from a Mono/.Net programmers' point of view and all this at very good performance!!!
I can't wait to get my hands on IronPython and play around with it!