This make programs in C/C++ is total BS.
Take a look at autocad, probably one of the most successful programs. In that case they took the embedding route. Main program is made in C/C++ embedded in side it is lisp interpreter. Blizzard and most other successful gamings companies embed lua. Firefox same story with javascript.
Or you can go the extending route this is the strategy used with python and ruby proggies. Make basic program with script, embed C/C++.
Ruby is very beautiful. It has many features which only lisp has.
Really nice thing is blocks and closures. Also besides scheme it has callcc. Callcc is super cool.
That all said, why do i use python

. Mainly because i am used to python, massive ammount of 3rd party libs for python. Ease at which python can interface with C/C+ libs.
Also ruby lacks a VM (they are working on one), if they ever get a proper VM i will switch over

One area of concern is threading. Threads in Ruby are dreadfully expensive and should be called ropes. They're still great to have, but they're not ideal in terms of larger scaling architectures. But as I've mentioned in the past, employing a non-blocking, evented approach to highly scalable architectures (
nested callback or Reactor pattern approach) offsets this thread performance loss.
Biggest issue is threads. Ruby threads are not "real threads" but what are called "green threads". Not having real threads only becomes an issue when doing stuff like GUI.
As a rule of thumb, no need to use threads. Reactor pattern is much better. In python the library of choice is twisted.