Having programmed a lot in Common Lisp in the past these comparisons between Ruby and Lisp kind of puzzle me. The things that make Lisp Lispy (i.e. homoiconicity, hygienic macros, quoting ) aren't part of Ruby. From my standpoint Ruby looks like most dynamic language these days in that strongly encourages highly stateful programming with a sprinkling of metaprogramming.
This is just a guess, but someone who only knows C++, Java and/or C# who learns Ruby (or Python, Perl, JavaScript, etc) and Lisp will find the two languages closer to each other than to what they know. I think that's why comparisons are drawn between the two frequently. Note that people have made the same observations about Python and JavaScript (Peter Norvig writing about Python, Douglas Crockford writing about JavScript)
In my experience, people who haven't programmed much in any Lisp think that higher-order functions and map, filter, and reduce are the essential elements of Lisp rather than homoiconicity.
Perhaps someone else has a different view?