The current documentation here: http://doc.crates.io/manifest.html states:

With the exception of the default feature, all features are opt-in. To opt out of the default feature, use default-features = false and cherry-pick individual features.

This is quite rigid, since it means you can't make a small adjustment to defaults - where a program may have multiple options which aren't related.

It also means if I use a 3rd party package with modified defaults, after an update I need to check if defaults where added which I might want to enable.

Note, I asked this question on stackoverflow, it was suggested to open an issue here:
http://stackoverflow.com/questions/39734321