While it took Spotify "a little bit" longer to finally support Windows Phone 8 (it was only released back in early February as a public Beta), Joe Belfiore unveiled today on Twitter that the public Beta will goes final today and will bring a couple of new features which were missed so far. Not yet available from the Windows Phone Marketplace, the new version is expected to feature more languages, offline playlist improvements and track scrubbing! Other than that, Spotify for Windows Phone is sporting the typical service features like search, browse & play millions of tracks, explore & play your friends' playlists, top artists and tracks, stream over WiFi or 2.5/3G - all your existing playlists are available.
Typically, Windows Phone app updates are stage-wise rolled-out and therefore it can take some time that you see the final version on your Windows Phone.
UPDATE: Spotify for Windows Phone 9 v2.0.4933.0 is now broadly available from the Windows Phone Marketplace (see link bellow)
Cheers ~ Arne