I haven't used a Mac in ages, so I'm unfamiliar with any unique features of Cocoa over what one gets with e.g. GTK+; what would you say the features that make it better are?
I'm usually a bit skeptical of current-generation GUIs (but then again, I'm ignorant of the Mac world) largely because it's usually so much more painful to extend and compose them. To pick a perhaps slightly unfair example (since it's basically about text processing), I use Weechat for chat rather than Pidgin, since the UI inconvenience of it being a CLI is outweighed by how easy it is to process my chat history, programmatically interact with notifications, and how much more functional Mosh/SSH are than X11 forwarding.
I'm usually a bit skeptical of current-generation GUIs (but then again, I'm ignorant of the Mac world) largely because it's usually so much more painful to extend and compose them. To pick a perhaps slightly unfair example (since it's basically about text processing), I use Weechat for chat rather than Pidgin, since the UI inconvenience of it being a CLI is outweighed by how easy it is to process my chat history, programmatically interact with notifications, and how much more functional Mosh/SSH are than X11 forwarding.