Lesson learned: Diagonal stripes, low contrast text, and angry fruit salad colors give me a headache.
There's a 3rd element that goes hand-in-hand with these:
Create an Account
Sign Up
Join
Become a Member
Sign in/out makes more sense to me because it focuses on user activities. Logs are back-end functions that users shouldn't have to think about.
I don't think it really matters much one way or the other, though I do like the list of sites and they way they have chosen. The only one I do not like how it does it is twitter, login/sign out... though with the recent redesign they have changed it to sign in/sign out.
I'd like to see some actual data on the relative usability. Maybe Nielson could take care of it.