I've started to read on the net that all browsers are implementing page zoom by default, not text enlarge.
I've also read a PrestaShop theming tutorial the other day that said...
Don't use ems anymore, thanks to page zooming. Use pixels for font sizes.
I'm not sure I necessarily agree, but with the body { font-size: 62.5% } for ease of em sizing, should we begin to phase out em sizing for pixels?
pixels for fonts is a bad idea. Your site will look crap on high dpi displays, and high density displays for the desktop are on the horizon (and are already on many mobile devices).
Pixel sizing can be more accurate, but scales to high resolutions and DPI badly. Browser AA does offset this somewhat.
Read Page Zoom, Elastic Layouts & Em might be helpful
Using em sizing has no negative effects for modern browsers, and removing it could create negative effects for old ones.
From a another perspective: I've found using em's much more restrictive which doesn't allow me to fiddle as much.
Additionally, desktop sized screens are not the only interface to the web. But, small devices are used to making good guesses. Therefore, I don't know if that's much of a concern.