That’s already a good idea, but here’s the clincher: When you hear a song that you like on one of XM’s 70 themed, ad-free music channels, one button-press records that song from the beginning — even if you were a little late hitting record. In all, this gadget can hold about 25 hours’ worth of recorded radio.

Image Credit... Illustration by Stuart Goldenberg

Long-suffering music fans could probably have predicted that XM would be sued over this glorious idea, and, well, sure enough. Maybe what’s so great about this idea isn’t so much its ingenuity as its bravery.

MUSIC BEAMING The Zune, Microsoft’s new music player, does something amazingly well that its rival, the iPod, doesn’t do at all: It lets you beam songs or photos wirelessly to another Zune. It’s easy and fast, and it could be a great way to discover new music recommended by your friends.

In practice, there’s more to the story. To avoid lynch mobs from the record companies, Microsoft designed the Zune so that beamed songs self-destruct after three plays or three days, whichever comes first — even, idiotically, your own recordings like college lectures and garage-band demos.

The Zune, therefore, is that classic case: a killer idea diluted by a ham-handed execution.

THE VIDEO-GAME WORKOUT Nintendo’s Wii game console, on the other hand, is a stellar product that succeeds precisely because its central idea is unencumbered by corporate baggage — and is tons of fun.

The masterstroke is its wireless controller, which detects the motion of your arm in three dimensions and in real time. As you swing, jab or whap through the air, your animated character on the TV screen swings the corresponding baseball bat, tennis racquet, fishing rod and so on.

(Perhaps it’s a bit much to suggest that this video game may actually help to address America’s problem of sedentary youth. But my own two in elementary school play the Wii’s tennis doubles game nightly with full-body vigor — and are perspiring after half an hour.)