Hm.. is this specific to the high resolution of the Retina display?

I think it may be inevitable for any pixel based image. When zoomed further than 100%, it is stretched. On a x years-old iPhone or Android no different.

Generalizing to all icons in the interface, at first sight it goes for:

• RSS/Atom icon: pixelated
• Collapsible navigation arrows: not pixelated but blurred (actually part of Vector extension not the core skin, but whatever)
• Enhanced recent changes arrows (part of common core, not Vector skin specifically)
  • These could probably just be CSS-styled htmlentities of arrows I guess?
• p-personal user icon (Tango Tango style)

Ah, I see there are already bugs for the others. No need to turn this into a tracking bug then. Reverting back to original case. (others are also blocking bug 32101, such as bug 35341)

Change 96197 had a related patch set uploaded by HectorAE:
shared.css: Start vectorizing common icons

https://gerrit.wikimedia.org/r/96197

direct link to the proposed svg feed icon. (looks good to me on Iceweasel (Firefox) 22.0a2 (2013-04-19))

https://gerrit.wikimedia.org/r/cat/96197%2C3%2Cskins/common/images/feed-icon.svg%5E0

Change 96197 merged by jenkins-bot:
shared.css: Start vectorizing common icons

https://gerrit.wikimedia.org/r/96197