In my mind there are a couple approaches to incorporating whimsy into interaction design: To bring a little dash of entertainment to a capability that already has to be there (e.g., jiggling icons on the iPhone), or to add something for the pure joy of it (e.g., Easter eggs in software).
In this first example, the whimsical element brings a bit of delight to a moment that could have been upsetting to users.
The Retro OutroThe litl can take the form of a traditional laptop, or be flipped into a easel configuration. This flexibility creates potential confusion because the hinge that enables the flipping has two buttons on opposite ends: One is the power button, the other is a menu/select button. When the litl is flipped between configurations, the relative position of the buttons swap left to right, making it easy to imagine pressing the power button when you intend to press the menu button. So we explored some solutions — a confirmation message, or maybe the double-press required by projectors. Both of these felt too "computer-y" for the litl experience.
When the power button is pressed, the video on the screen begins to compress vertically. If you keep holding the button, the video compresses down to a single dot and the litl turns off, just like older CRT TVs — hence, "retro." If you release the button before the video compresses completely, the video springs back to full screen and the litl stays on. One of the keys to making this work is it's responsiveness. (The litl development team did a great job of tuning the feel.)
The GiggleThe other whimsical detail we added just for the fun if it. If you press both of the buttons on the hinge at the same time, the litl will giggle, as though you've tickled it. It's just a fun element that further emphasizes that the litl is different that other computers and has a personality all it's own.
It can be hard to work whimsy into enterprise applications and tools that people use all day. That extra little bit of entertainment usually comes at the cost of speed and efficiency. But for consumer products it may be worth considering some whimsical solutions to sticky design problems, or just adding some fun surprises. It's a great way to create an atmosphere and experience that becomes a deeper kind of branding.