I just stumbled across Reg's blog today after a link from Jeff Atwood's. Almost immediately I found this post about turning strings into procs in Ruby. Wow.
One of the only things about Ruby that consistently bugged me was the difficulty of passing existing functions into methods expecting blocks without having to wrap them in boilerplate junk. This (and Symbol#to_proc) basically cleans all that up.
He also has a nice implementation of unfold posted.
IronRuby can't get here fast enough.