I'd like to try my hand at some PC game development.  I keep hearing that python is slow compared to C++.  Is this something I should be worried about?  
I am more familiar with python than C++.  If I'm looking to make some games, should I take the time to learn C++ or just stick with Python?
The kind of game matters immensely. High performance games like the big name PC or console games are almost exclusively the domain of C++.
Casual games can be written in almost any language, including slower languages like Python.
If you're a garage type developer who gets his hands wet with some simple game development for this first time, Python would be more than enough. If you however have the ambition to work for a game developer studio, I would definitely recommend learning C++.
How "slow" is python for game development?