I also see this post explaining the presence of the -webkit-background-clip (http://tumble.sneak.co.nz/post/928998513/fixing-the-backgrou...), but I don't see that behavior in Safari 5. Potentially fixed? If not, I would certainly add that to my boilerplate.
In SCSS I use a very simple mixin for rounded corners, something I use frequently when designing sites.
Then in the class just add: