The result is that Safari and Firefox
still resize the text, whereas IE6 and
IE7 do not. The text can be resized in
Opera and IE7 by using the page zoom
tool, which magnifies the page layout,
text and images within.
Text size in ems iteration 2
The results show that, across all
browsers, text at the medium browser
setting is rendered identically to
text set in pixels. It also
demonstrates that text sized in ems
can be resized across all browsers.
However IE6 and IE7 unacceptably
exaggerate the smallness and largeness
of the resized text.
Body sized as percentage iteration 3
The results show that the difference
between larger and smaller browser
settings in IE6 and IE7 is now less
pronounced, meaning we now have all
browsers rendering text at an
identical size on their medium
setting, and resizing text
The results show that the 18px
line-height is inherited by all text
on the page....Unfortunately the
results show that the 18px line-height
is not scaled by IE6 and IE7 when text
is resized, meaning the largest
setting appears to squash the text.
The results show accurate,
consistently resized text and
line-height across all browsers.
Perfect. Or nearly so.
The Safari monospace problem iteration 6
The results show consistently resized
text and line-height across all
browsers, including the monospaced
text in Safari 2.
Even though this article is dated 2007, it's still very much relevant. Setting font sizes is more than just setting an em (or px).
This answer doesn't address the question, and the link (whilst interesting reading) can't be considered relevant when the browsers concerned are at least one major version on from where they were in 2007.
Your question is whether using ems to size fonts is still considered worthwhile. The answer is conditionally yes, but only when applied with other means. Setting line height, for example, ends up being likewise important. Consequently, using ems only partially solves the issue. In terms of Chrome, FF3, IE8, the article still applies. Yes, it is old, but is still relevant.
So, it's all IE 7 AND 6. 6 is dying, 7 is on it's way there - who cares? Safari 2? I'll just use pixels.