I’m fascinated with the concept of a "mashup." It’s a technology that allows developers to leverage existing applications and services to achieve a kind of hybrid result. A prime example would be the combination of a map service, such as Live Maps, with a shopping/auction service, such as Live Expo, to create a hybrid application that could display the geographic location of each offered item. Our benevolent benefactors at Microsoft have even put together a nifty online tool called Popfly, which allows developers to cobble together a mashup without writing much (or any) code.
Of course, the mashup is nothing new; it just goes by different names in other venues. Businesses call it "synergy." Recording artists call it "sampling." Filmmakers call it "inspiration." Writers just label it "plagiarism." I figure that there are a finite number of ideas in the universe, so chances are that you’ll eventually stumble over someone else who’s said/played/written it before. Your best hope is just to improve the expression of an idea, or create a mashup.
Wordsmiths have been creatively building mashups for years. Instead of inventing new words, why not just take the best parts of root words and create something altogether new? Thanks to mashups, we have new words like "PowerPoint," "appletini," and "Pokémon."
The principle difference is that Web mashups don’t just happen by accident. Complex program interfaces have to be exposed to "hook" into each other, so Web applications have to be carefully designed to facilitate mashups.
If you’d like to read more about mashups, check the Wikipedia article on the subject.