Also, after launching a feature, we have to go back in the code base and remove the old version (maintaining separate versions of all features on Flickr would b

Also, after launching a feature, we have to go back in the code base and remove the old version (maintaining separate versions of all features on Flickr would be a nightmare). But overall, we find it helps us develop new features faster and with fewer bugs. Its crazy to me to think that a high profile site like flickr would push impure code into production with the promise of "we'll clean it up after launch". I guess if you've got the right culture and discipline, it can work. Just seems so fragile.