Touchscreens and Hover
One issue I haven't seen discussed much is the impact of touchscreens on how we design web pages. The most obvious issue is that for an iPad or iPhone user there is no such thing as "hover" or "mouseover" - in software-speak, touchscreens do not support mouseover.
For Web designers and CSS themers, this is a very big deal. What would you say is the number one user interface mechanism in CSS? I nominate our beloved pseudo-class, hover. We use it to let the user know when the mouse is hovering over a link or other interactive feature. It's our primary way of adding vitality to a web page.
With the touchscreen, it's gone. The mouse, which was invented in the early 1980s, was designed to be a McLuhan-esque extension of our hand, a way for us to "touch" the elements of a computer's graphical user interface (a phrase that has earned its own acronym, GUI). The mouse allowed us to push virtual buttons in the GUI. Since a mouse is multi-dimensional, i.e. it has at least two properties (position, and up or down), an interface could be programmed to indicate when the mouse was positioned over a button (mouseover) and could initiate some action when the button was pushed (mousedown, or click). The touchscreen interface has fewer dimensions. It's binary, if you will. The finger is either touching the screen or it isn't. The touchscreen introduces some new gestures such as scrolling and zooming, but it takes away the hover.
As themers, we're used to accommodating various "user agents" - in some cases bending over backwards and sideways, i.e. IE. So this is just one more thing to consider. One more doodad to add to the graceful degradation progressive enhancement grab bag. If we check our logs and compare user agent percentages, we'll see that touchscreens are an increasing share. How much their share will be remains to be seen. I understand that there are some patent disputes now in litigation with Apple claiming exclusive rights to some touchscreen technologies. No matter the outcome - Apple will either lose or license - touchscreens will become more and more ubiquitous.