The people behind Opal are really awesome. I've spoken to them a few times about this project and they really do know their stuff. Opal looks very promising to anyone who's still using Ruby.
How easy is it to call native javascript libraries with opal? Having to write wrapping code stinks.
This is what coffee script should have been!
I see the benefits of Opal, but can anyone enumerate the downsides? I imagine it generates quite a bit of cruft as CoffeeScript does (of course, one argues that developer satisfaction in using said language outweighs the extra lines added to JS files).