I have been looking at the Ruby programming language recently. I like
Ruby and would like to use it myself but I see some several key
limitations that hinders use of Ruby in mainstream projects (and makes
it hard for me to recommend it for my customers):

   1. Slow and very primitve VM - no jit, vm comparable to java 10
years ago.
   2. No native thread support - this is increasingly a problem as
threading and multi-core technology becomes the norm (*)
   3. No (first-class) unicode support (*)
   4. Poor development enviroments compared to .NET/Java - however this
is slowly getting better - f.x. RDT is quite useful.

For more info see my blog at:
http://mortench.blogspot.com/2005/11/investigating-ruby.html

This is not a flame-invitation, but I would be interested in hearing
constructive feedback from more experienced Ruby developers to address
wrongs/shortcommings in my analysis.