A recent study measured the productivity of using Python+Django vs. C#+ASP.NET, in terms of user-stories per week. The results are that 1 Django developer is equivalent to 2 ASP.NET developers, productivity-wise:

http://kurtgrandis.com/blog/2010/02/24/python-django-vs-c-asp-net-produc...

The Django team that participated in the benchmark, BTW, had no prior experience with Django, which probably implies that the difference can be even higher.