As you can see in the screenshot below, the current
17px is too low. After a try with firebug, I'd suggest to use a minimum
line-height must not have a unit. It's just a multiplication factor of the font size... (currently set for this definition:
tr.comment > td in all.css acc. to firebug). I'd suggest to set it to
1.5. You could also reduce the top/bottom padding for
a.comment-user.owner (which currently overwrites
a.comment-user for some reason).