Shouldn't be too difficult. At it's core, OS X is just a modified version of FreeBSD, which is a close cousin to Linux, so you'll feel right at home there.
But for better or worse, Apple has traditionally lead the way in terms of UI design, so I think you'll find that OS X looks and behaves a lot like KDE or GNOME on Linux. The one big "gotcha" to be aware of, is that on OS X, closing the last window of an app doesn't close the app. You have to specifically close apps.
If I'm competent with Linux will it be an easier transition from Linux to OSX?
I've been using PC for my whole life.. So yea.