My main disappointments in Ruby so far have been the lack of autovivification in multi-dimensional arrays (doing dynamic programming without it is a PITA)
Curiously not something I've ever had problems with. I guess I've wrapped stuff up in an object before I need multiple levels of indirection so the autovivification stuff never hits me.
and the available documentation not meeting my expectations.
Buy the Pickaxe book. It's well worth the money.
Ruby does make me appreciate the "Huffman coding" of Perl.
I think that this depends on what you're doing. I'm finding my Ruby tends to be more concise than my Perl 5.
(Happily using Ruby in the real world :-)