This caught my attention last night.
On the latest ALT.NET Podcast Scott Bellware discusses how as opposed to Ruby, languages like c#, java et al. are not truly object o
You asked: "Can someone show me an example of a wonderous thing I could do with ruby that I cannot do with c# and that exemplifies this different oop approach?"
One good example is active record, the ORM built into rails. The model classes are dynamically built at runtime, based on the database schema.