Hover states are a big one. Also making call-to-action targets bigger for the less precise pointing device (ie, your users' fat fingers). Making sure you use Flash fall-forwards with HTML5 video/audio available for iPad / non-flash devices.
iPads and iPhones also have great support for CSS3 transforms (3D included with hardware acceleration), but some of the other "common" CSS3 and HTML5 technologies do bog down on the slower processor. Your average desktop may not have a dedicated video card and a browser with hardware acceleration, which creates a smaller intersection of features that will work with no brains on iPads and (generic) desktops.
The list, of course, goes on, and it will continue to grow with time. As with the well known deficiencies of IE (floating, clearing, zindex bugs, etc) however, the iPad caveats and corner cases are becoming more of a known quantity. As with IE, just takes a bit more planning.
> Making sure you use Flash fall-forwards with HTML5 video/audio available for iPad / non-flash devices.
Can't you for the love of all that is binary do it the other way around? I hate it when sites push Flash on me on the desktop when there's a pure html version ready a user agent string away.
Desktop browser support for h.264 video via HTML5 is a crap shoot. Sometimes it works well (Safari), sometimes it works poorly (Chrome), and sometimes it doesn't work at all (Firefox and IE9-).
I think he's just asking for a flash fall-back if native playback through HTML5 isn't supported. Maybe that is what "fall-forwards" already meant, but I'm not too familiar with that term...
iPads and iPhones also have great support for CSS3 transforms (3D included with hardware acceleration), but some of the other "common" CSS3 and HTML5 technologies do bog down on the slower processor. Your average desktop may not have a dedicated video card and a browser with hardware acceleration, which creates a smaller intersection of features that will work with no brains on iPads and (generic) desktops.
The list, of course, goes on, and it will continue to grow with time. As with the well known deficiencies of IE (floating, clearing, zindex bugs, etc) however, the iPad caveats and corner cases are becoming more of a known quantity. As with IE, just takes a bit more planning.