[LinaLauneBaer]

Collisions are very very rare. In over 10 years of Objective-C development I have maybe seen it once. Also: clang got much better at detecting collisions at compile time (where possible).

That said: Swift extensions are safer because private categories cannot collide.

[_cbsz]

Try OBJC_PRINT_REPLACED_METHODS sometime. It's frightening. (http://stackoverflow.com/questions/9466732/in-objective-c-ho...)

[spiralpolitik]

This has been my experience as well.