Here’s the Ruby In Steel editing / debugging experience. Intellisense works dynamically — as soon as you define a function, it becomes available to Intellisense. The debugging experience seems to be the standard VS one (that is, pretty darned good).
REPL functionality is provided by IRB in a console window: not ideal, but convenient. There’s quick access to Rails, Rake, and Gems (see the second screenshot).
The install silently guessed wrong on my Ruby install location, which caused my very, very first “puts 2+2” to fail, but it was easy enough to guess that the issue could be fixed under Tools | Options…
So far, so good: more to come as experiences develop. I look forward to putting this head-to-head against Komodo.