Eelco recently wrote about using subdomains in Rails, outlining a seemingly neat idea about having them as subdomains in production but using paths in development. It is clever and looks very usable at first sight. It’s also a very bad idea that is likely to get you side effects you really won’t be happy about. I normally don’t do “rebuttal” posts, but in this case — since I have dealt with that problem before — it feels warranted. Without being too lyrical about it, I want to o...