X server versus native OS X 10.xx support

[Karl Pongratz <karlhp karlhp com>]

Hi,

I am a newcomer to GTK. As far as I understood there is no native OS X 
10.xx support and it requires to install X server.
Two questions.
1.) Are there any performance or other drawbacks when using GTK on  OS X 
with X server?
2.) Can X server be installed together with the program or does it need 
to be installed by the user?

Many thanks for any help.

Karl