Kanwei's post has some questionable points that Pablo rightly picks up on (being forced to use ternary operators?) and some that he doesn't ("LOC matters, people.").
Just like Kanwei, some time ago I decided to ditch Ruby and focus on Python for the tasks that I would normally use Ruby for. The two final nails in the coffin for me were
The redcloth library - a textile-markup-to-HTML library, which is well presented and documented. I looked under the hood and reeled in horror away from the "parser" which was implemented in terms of regular expressions and big loops. I felt this spoke volumes about the quality of code coming out of the Ruby community.
Interestingly, Pablo cites rubygems as one of the points in favour of Ruby.
Whilst both Pablo and Kanwei mostly focus on technical details for their attack and defence of Ruby, these two points for me were largely social, community issues.