Subscription music services have been on-line for more than a decade - old timer Rhapsody launched in 2001. But nobody's jump started the concept of an "all you can eat" internet music buffet  quite like Swedish-import Spotify, which joined the US fray last year and upped the game again today with the launch of its custom iPad app.

Designed to convert users of the free, ad-supported version of Spotify playable only on computers, the iPad app requires a $10 premium subscription, but is truly a thing of beauty and discovery. (Spotify claims ten million active users worldwide, three millon of whom are paying.)

Start with razor sharp graphics of album covers and a smooth, fast touch screen operation to calm even the most impatient of trigger fingers. No old school juke box has ever jumped "on a dime" like this app does from song to song, album to album, with butter smooth crossfades.

The multitasking Spotify iPad app offers lots of clues to what's hot in the music world, not only with selections of new releases and chart toppers from the likes of Gotye and Katy Perry,  but also by sharing playlists and tunes that are "trending" among Spotify users - both friends and  strangers in the neighborhood. You can really get into the social aspects of music by linking a Spotify account to your Facebook address, thereafter communicating everything you're playing.

Spotify discovery tools also include automatic suggestions of affinity artists (if you like this one, you'll also like . . . ) And it often summons  up a  lengthy biography of an artist to read whilst you're digging  the music -on the iPad's internal speakers, headphone-jacked sound boomers or beaming wirelessly to Bluetooth and Apple Airplay-enabled sound systems.

Last time I looked at Spotify, its' catalogue came up short compared with Rhapsody and even MOG, another relative newcomer. The latter two are still the superior performers when it comes to serving up fringe categories like jazz, classical and world music. But for new contemporary releases, the three are more simiilar than not.

This week, all three are spotlighting (among others) the new Train set "California 37," a new EP by the Raveonettes,  the Beatle-y  (and good) Brendan Benson release "What Kind of World," the shockingly fine. lost-and-found collection from Luther Vandross "Hidden Years" and the much buzzed about debut from Alabama Shakes, "Boys and Girls.

But there were some holes. A new Dirty Dozen Brass Band set "Twenty Dozen" is found on Rhapsody and MOG, not at Spotify. Same goes for Rufus Wainwright's most pop minded "Out of the Game."  Warren Haynes' southern rock scorcher "Live at the Moody Theater" showed up on MOG and Spotify, though not on Rhapsody. The British funk jam band Jamiroquai's "Rock Dust Light Star" and British pop set "Give To the Wind" from  The Maccabees get home page love on Spotify, then only showed up on Rhapsody with a search and not at all on MOG.

In terms of eye candy, the iPad apps for Spotify, MOG and Rdio (another streaming music service with free and pay options) are all equally attractive. By contrast, what you get on the iPad as a Rhapsody subscriber is the same minimalist, partial screen (but zoomable) menu available for the iPhone and Android mobiles.  Clearly, Rhapsody wants to remind us that its' service is available and focused on smartphone streaming and downloading while Spotify is not. Still, the old pro needs to up its game, if it wants to grab the kids.