One of the biggest problem for dynamic language (say python) is design time support.
For example, in C#, after you define the
datatype for ISomething, when you type the
variable name, the editor can pop up a list
of functions that are available for this
variable. In python, you have to look up
the document to see what function is supported since datatype is determited at
runtime. The same is true for a good
GUI builder system.