Python is used widely and pretty heavily.
It's a built-in feature to many operating systems in common use. The exception, of course, is Windows.
I just found out -- the hard way -- that Python 2.6 is an integral part of Apple's iLife suite of products.
Important safety tip for Mac OS X users. System.Libary.Frameworks should not be touched.
Also, it helps to get used to the idea of typing python3 on the command-line. Further, it helps to skip Python 3.1 and go straight to Python 3.2.