I know that this is a difficult question to answer, but I thought I would try anwyays....
I am just starting at a new company where they have a minimal existing code base.  It probably has a month of man effort invested at this point. It is currently written in Ruby.  
It is also currently using Ruby on Rails -- but mostly just for the sake of testing out the Ruby code. 
The ultimate goal of the code is actually to drive a backend to a site that will be written in php (could be a backend to Drupal, Echo, etc...).  
I have no experience with Ruby, so I would tend to want to go with a language I know better (like Python), but am not willing to rule Ruby out for no reason.
If you are not going to use Ruby for a Rails project, is it still worth it?  Will I be better off going with Python or some other language?
How do the libraries stack up?
Thanks!!!
Using Ruby für two years now , i find it powerful, easy to learn, having good libraries, good community.
But how should we know if it fits your needs? Try it an you will find out.
To Ruby or not to Ruby