So I'm aware of the big ammount of general-purpose scripting languages like Ruby, Python, Perl, maybe even PHP, etc. that actually claim being usable for creating desktop applications too.
I think my question can be answered clearly

Are there actually companies using a special scripting language only to create their applications?
Are there any real advantages on creating a product in a language like Python only?
I'm not talking about the viability of those languages for web-development!
Should I stick with C(++) for desktop apps?

best regards,
lamas
Python (combined with PyQt) is a very solid combination for GUI desktop applications (note that while QT is LGPL, PyQt (the Python bindings) is dual licensed: GPL or commercial).
It offers the same (GUI library-wise) as Qt on C++ but with Python's specific strenghts. I'll list some of the more obvious ones:

rapid prototyping
extremely readable (hence maintainable) code

Should I stick with C(++) for desktop apps? 
In general: no, unless you want to / need to (for a specific reason).
"Real" and non-embedded use of Ruby, Python and their friends