As reported on IRC:
Enabling $wgHandheldForIPhone seems to break Monobook-based skins and cause them to not load their CSS. Non MB-skins seem to be unaffected, and non-IE browsers seem unaffected.
Adding Brion as a CC since the skin updates for the iPhone were his baby.
Version: unspecified
Severity: normal
Platform: PC
Per notes on http://www.alistapart.com/comments/returnofthemobilestylesheet/?page=3 and elsewhere it looks like IE doesn't handle media type specifications properly; a CSS 2 browser *should* see the 'screen' in the 'screen and (min-device-width: 481px)' and render that style for screen.
Annoyingly there's no sign of this information on Apple's docs which recommend the CSS3 media query in the first place: http://developer.apple.com/safari/library/documentation/AppleApplications/Reference/SafariWebContent/OptimizingforSafarioniPhone/chapter_3_section_2.html
IE conditional comments can be used to work around this by listing a media-less <link> for IE and the media-queried ones for everyone else.
Alternately, we could move to a model where iPhone and similar high-end mobile browsers get a _supplemental_ style sheet which adjusts some sizes and such instead of the completely separate handheld-only style. This might actually be ideal, since we have a completely separate web gateway for a fully-handheld-optimized version of the site.
Closing. wgHandheldForIPhone was removed by 1965df8df3844ea62e409a34b1e971f66ac9a74a .