Since Safari updated to v5.1, for whatever reason, Radio Buttons in the ACP now appear to be cut off along the top. See attached image.

Anyway, a simple fix is to add a tiny bit of margin as

margin-top:1px;

to the input.radio style element in admin.css

This would not only repair the issue in Safari 5.1, but would be a harmless and un-noticed effect in all other browsers.