Nice tool! Shadow tables are quite convenient as they support arbitrary ALTER TABLE statements but they also seem a bit wasteful to me. I'm working on a similar tool called Reshape (http://github.com/fabianlindfors/reshape) which instead uses temporary columns to reduce the time a migration takes and the extra storage necessary.
Yeah I agree, it's certainly a bit wasteful, especially during the operation. You can clean up the table automatically in the end with --drop. Love the concept and path with Reshape btw, I think its very innovative.
