I think relative font-sizing with "em" and "rem" [1] is a popular and good choice these days. "em" has been popular since 2004 after an article by Rutter [2].
IE9- (and Android 1.6-) didn't scale/zoom well when the font was set in px. But using px was widespread despite these (and other) cons because it was easy, reliable and consistent to implement across browsers. [3]
Pt (point type) are only for printer style sheets [4], not screen style sheets. Using them for screen styles is not-done and doesn't make much sense. [5]
IE9- (and Android 1.6-) didn't scale/zoom well when the font was set in px. But using px was widespread despite these (and other) cons because it was easy, reliable and consistent to implement across browsers. [3]
Pt (point type) are only for printer style sheets [4], not screen style sheets. Using them for screen styles is not-done and doesn't make much sense. [5]
[1] http://snook.ca/archives/html_and_css/font-size-with-rem
[2] http://clagnut.com/blog/348/
[3] http://alistapart.com/article/howtosizetextincss
[4] http://css-tricks.com/css-font-size/
[5] http://style.cleverchimp.com/font_size/points/font_wars.GIF