I’m noticing on Can I Use that all modern versions of major browsers used in the US now support the non vendor prefixed versions of the CSS3 properties: border-radius and box-shadow. Is it safe to stop using the vendor prefixes for both of those properties now?
That depends on your user-base. While newer versions of popular browsers do support non-prefixed versions, older versions do not. You can't be sure that all your users have already updated or will ever update their browsers.