If one is going to use playful labels for things, there must be a way to find out what the "fun" feature does. In my opinion, Google gets it wrong by not providing any sort of documentation on this feature (other than this old blog post). What's more, they've apparently broke the feature with their recent redesign, so that's a problem, too.
My favorite examples of "quirky" interface options on the travel search engine Hipmunk (which, if you haven't tried it, has the best UX of any travel site I've ever used, hands down). On their flight searches, the default sorting mechanism is "Sort by Agony", which is clearly and succinctly defined in their FAQ:
What is Agony, and why would I want to sort by it?
We know that price isn't the only factor that goes into purchasing a flight. While other sites sort by price, Hipmunk automatically sorts results by "Agony," which is primarily a combination of price, flight duration, and number of stopovers.
Likewise, when one searches for hotels, the results are sorted by "Exstasy":
What is Ecstasy, and why do I want to sort by it?
Similar to our Agony sort with flight search, we recognize that price isn't the only factor that goes into buying hotels. We sort by "Ecstasy," which is a combination of price, amenities, and reviews.
Two specific things make this work for me:
- It's Hipmunk's "secret sauce". Much like Google's algorithmic prowess merges a bunch of factors into an overall ranking that is generally right, so to does Hipmunk. It's the equivalent to "PageRank". As other answers have noted, "Magic" is really just "recommended for me", so giving it an unknown name can just be confusing for users (and thus the feature isn't used).
Hipmunk clearly communicates what they mean. When you mouseover the selector, you immediately get a clear, concise description for what it is:
Additionally, they use the loading time effectively, teaching new users how to use the unknown interface elements (the things that set them apart from other travel services:
The bottom line: Having quirky/playful/fun interface elements is great, but only so long as it enhances the user experience. In my opinion, Google Reader's example is a distraction, not an enhancement.