Ruby is over ten years old, now and rising in popularity (as it deserves :) With 1.8, Ruby is improving steadily.
I like the fact that it is interpreted (which gives the language its incredible flexibility), the "Principle of Least Surprise" (most surprises I get are pleasant), the proper abstraction, the closeness to the underlying platform (and the easy C-bindings), the iterators and blocks, the automatic Bignums, the lack of char, the portability and the default libraries provide what I need (The Ruby Application Archive contains more libraries and applications. So far I found all bindings I needed.
Initially, I was a bit set back by the dollar for global variables, the at-symbol for instance variables, the colon for symbols. But they indicate scope really well (and that's actually very useful when reading code).
Due to it's flexibility and runtime-only checks, people claim Ruby isn't suited for large projects. I disagree. A colleague of mine called Ruby "superglue", indicating it is a perfect language for large projects. You wouldn't fool yourself into believing you solve large problems with only one programming language, would you? Upon that, you can put more logic in less code when the code is written in Ruby: it will actually make your large projects smaller.